Figure 2, which is critical to the findings of this publication, presents an intra-individual group relationship; laboratory studies regarding the influence of dehydration on exercise performance utilize an individual as his/her own control. The cross-sectional trend in Figure 2, which arose from a single field study, should not be equated with a randomized, controlled, repeated measures experimental desig...
Figure 2, which is critical to the findings of this publication, presents an intra-individual group relationship; laboratory studies regarding the influence of dehydration on exercise performance utilize an individual as his/her own control. The cross-sectional trend in Figure 2, which arose from a single field study, should not be equated with a randomized, controlled, repeated measures experimental design.
On the basis of Figure 2, the text states, "... lesser degrees of body weight loss were associated with longer race finishing times..." and the Discussion section implies cause-and-effect. However, statistical correlation neither implies causation nor warrants a principle. Figure 2 also includes noteworthy exceptions. Three runners (upper left quadrant) lost approximately 4 - 7% of body weight (i.e., 2.9 - 5.1 kg, based on a prerace body weight of 72.2 kg) but finished with times >300 min; and
three runners (lower right quadrant) gained 2 - 3% of body weight (i.e., 1.4 - 2.2 kg) but finished with times approximating 180 min. Further, percent body weight change accounted for only 4.7% of the variance in race
time (r2 = 0.047). We believe that this relationship is weak because endurance exercise performance is influenced by training, diet, psychological state, years of experience, age, and numerous other factors which interact in complex ways 2. Further, the 2009 Mont Saint-Michel
marathon was run in air temperatures ranging from 9 to 16?C (Table 1). In a hot environment, runners who drink less (i.e., 6% of runners lost 6 - 8% body weight loss, see Fig. 1) increase their risk of exertional heat exhaustion and heatstroke 4. This medical advice is noticeably absent, as
a qualification to the concept that "the fastest runners lost the most weight".
Three other factors likely complicated the relationship between body weight change (%) and race time (min). Firstly, approximately 78% of the 643 runners lost weight. Sweat loss, of course, was part of their total
body water deficits, but was not considered in the interpretation of Figure 2. Similarly, we note that pre-race excretion is not mentioned. This would amplify reported body weight changes because runners void bladder and bowl as the race start nears. Body weight was measured
between 90 and 60 min before the race, and thus weight loss due to pre-race elimination of urine and feces was unknown in Figure 2. Thirdly, we examined numerous online photos of competitors in the 2009 Mont Saint-Michel marathon. On the basis of our previous experiences at marathon events, we expected that front runners would wear less clothing than slow runners. This trend was evident. Thus sweat-soaked clothing, which had been dry at the starting line, represented an additional unmeasured component of the body weight variance in Figure 2.
Much text concerns drinking, biological signals and thirst, however none of these variables were measured during the present study. Thus it is invalid and speculative to state, "... athletes will not wilfully (sic)
ignore their thirst when fluid is available in excess...", or to state, "... the only conclusion can be that these 'dehydrated' athletes were drinking according to their innate biological signals..." What evidence
supports these statements besides a range of body weight change? It is widely appreciated that athletes ignore innate biological signals (e.g., pain, fatigue, perceived exertion) during competition, to optimize performance. This issue is further complicated by the fact that thirst sensation and drinking behavior are influenced by numerous host factors (e.g., stomach distention, plasma osmolality, oropharyngeal reflexes), the environment, and fluid characteristics (e.g., saltiness, sweetness) 3.
Therefore it is impossible, from the data of Zouhal et al. 1, to formulate substantiated conclusions about the relationship between body weight change and thirst, or between performance and thirst.
Fluid overload and illness are considered in the Introduction and Discussion sections. However, these concepts are misplaced, in that neither symptomatic exertional hyponatremia (EHS) nor fluid intake were
reported for any of these 643 runners, including those who gained 3 - 4% of body weight (2.2 - 2.9 kg, Fig. 2). Because the data of this paper focus on performance, not illness, and because > 90% of participants did not gain weight, we believe that the following question is more
relevant to competitors, "Is finish time faster or slower when a runner is mildly dehydrated (1 - 2% body weight loss) than when she/he is severely dehydrated (>5% body weight loss)?" It is impossible for group trends
(Fig. 2, Tables 3 and 4) to answer this question.
Finally, the interpretations of Tables 3 and 4 (which present the same concept, in reverse order) fail to consider differences between the fastest and slowest runners. Exercise intensity and duration affect the
volume of fluid consumed during a race. Front runners (i.e., those who finish 42.1 km in 160 min) experience a high ventilation rate (e.g., >120 L/min) that precludes consuming water, out of concern for inhalation and coughing; they also are conscious of time spent at aid
stations. In contrast, back-of-the-pack runners typically spend more time at aid stations, drink more often, walk during part of the race, and have a greater requirement for exogenous carbohydrate (i.e., 30 - 60 g*h-1, mostly in fluids 5) because they are on the course for more than 5 h.
Thus, we believe that an alternative interpretation (i.e., "During a marathon, fast runners drink less than slow runners.") is superior to the published conclusion, "body weight loss during a marathon race may be
ergogenic".
References
1. Zouhal H, Groussard C, Minter G, et al. Inverse relationship between percentage body weight change and finishing time in 643 forty-two kilometere marathon runners. Br J Sports Med, published online December
15, 2010 as 10.1136/bjsm.2010.074641.
2. Leyk D, Erley O, Gorges W, et al. Performance, training and lifestyle parameters of marathon runners aged 20-80 years: Results of the PACE-study. Int J Sports Med 2009;30:360-365.
3. Johnson AK. The Sensory Psychobiology of Thirst and Salt Appetite. Med Sci Sports Exerc 2007;39:1388-1400.
4. Armstrong LE, Casa DJ, Millard-Stafford M, et al. American College of Sports Medicine position stand: Exertional heat illness during training and competition. Med Sci Sports Exerc 2007;39:556-572.
5. Coyle EF. (1999). Physiological determinants of endurance exercise performance. J Sci Med Sport 1999;2:181-189.
Please check www.ligmaster.com for info on an ankle, knee, elbow and shoulder non-radiographic arthrometer that quantitatively determines the percentage tear in all of the clinically important ligament of the above joints.
I am afraid a little disappointed with this review. I take
issue with the premise that osteitis pubis and osteomyelitis could
possibly be considered in the same review. As correctly identified in the
piece, one is acute and one chronic with different predisposing and
underlying pathology.
Further more, although the relevance of Level 4 evidence is challenged,
there is little comment on either the diagnostic criteria, the...
I am afraid a little disappointed with this review. I take
issue with the premise that osteitis pubis and osteomyelitis could
possibly be considered in the same review. As correctly identified in the
piece, one is acute and one chronic with different predisposing and
underlying pathology.
Further more, although the relevance of Level 4 evidence is challenged,
there is little comment on either the diagnostic criteria, the actual
outcome measures used in resolution, and hence the comparability or indeed
homogeneity of studies.
At best this really represents opinion and the authors elected to exclude
one paper on adductor related groin pain but make little reference to the
diagnostic methods employed to ensure what was termed as OP was indeed
this and not either non specific groin pain or pubic bone overload.
I would have preferred a more inclusive approach to non specific groin
pain, rather than the assumptions made, which would have been a more
useful review. The take home message could be misinterpreted as the
"benefits of prolotherapy in non specific groin pain based on a single
study".
I fully agree with the comment from Dr Creaney regarding PRP.
Unfortunately, there is little sound clinical science supporting the use
at the moment. The design of studies published so far has been far from
perfect. The studies with poor design have tended to produce good results,
whereas the RCTs with proper design have shown less of an effect. Another
challenge is the multitude of unknown clinical variables such as amou...
I fully agree with the comment from Dr Creaney regarding PRP.
Unfortunately, there is little sound clinical science supporting the use
at the moment. The design of studies published so far has been far from
perfect. The studies with poor design have tended to produce good results,
whereas the RCTs with proper design have shown less of an effect. Another
challenge is the multitude of unknown clinical variables such as amount of
PRP, number of injections, when to inject, where to inject etc. In our
paper, we citically evaluate current use of PRP and call for proper, well
executed clinical research.
I congratulate the IOC Consensus panel on having produced as clear a
summary of the current understanding of the basic and clinical science
relating to PRP as the body of published literature allows. While there
was initially great hope in Sport Medicine circles that PRP would become
the magic bullet for injuries, recent trials such as de Vos [1], have failed
to provide that conclusive evidence so de...
I congratulate the IOC Consensus panel on having produced as clear a
summary of the current understanding of the basic and clinical science
relating to PRP as the body of published literature allows. While there
was initially great hope in Sport Medicine circles that PRP would become
the magic bullet for injuries, recent trials such as de Vos [1], have failed
to provide that conclusive evidence so desired.
This is not surprising. The more we learn about tissue regeneration,
the more apparent it becomes how complex a process it is. Tissue
regeneration is not a passive phenomenon, instead it is a highly co-
ordinated interplay of multiple cell lines at different stages of
maturation. Different cellular and humoral components play their different
roles.
The process can be likened to the repair of a collapsed building. Consider
muscle injury. The initial cells on scene, due to bleeding, are platelets,
but they appear to be relatively passively involved - alarm bells which
sequester and awaken the major players. Platelets release chemotactic
factors which attract neutrophils to clear the debris [2,3]. However within
24 hours macrophages [4] arrive, akin to the foreman, and it is these cells
that appear to regulate the process from this point onwards. If there is
any 'brains' or 'thinking' to tissue repair, it would seem to be the
macrophages doing it. Next come the actual builders. Fibroblasts are
activated to produce a collagen infrastructure, and satellite cells, to
form myocytes and finally myotubes, merging to become a single strand of
muscle fibre [5].
So where do 'growth factors' come into it? These proteins are simply
the communications being sent between the foreman and his workers. The
messages are very simple - move or stay put, divide or don't divide, live
or die, make collagen etc. In biology we use the terms chemotaxis;
mitosis; quiescence; apoptosis and protein biosynthesis. The point is this
- growth factors are just the messenger molecules used by one cell to send
an instruction to another, they are not the person giving the orders.
Unfortunately the 'language' of growth factors is very different to
English. We are used, pretty much, to one word having roughly one meaning.
However growth factor 'words' are more like a tonal language, Mandarin. In
these languages the same word can have multiple different meanings
depending on how you pronounce it. In the same manner, growth factors can
produce varying effects depending on their concentration, time of release,
point in cell cycle and recipient cell. Thus trying to pin any one growth
factor down to one particular action can be pointless - TGF-?[1] is commonly
associated with fibrosis [3,6,7], but it can stimulate regeneration or
fibrosis, chemoattraction or stasis, depending on its concentration [8],
target cell, and sequence within the tissue regeneration process.
Moving back to the analogy, it requires a great deal of intelligence
to rebuild a collapsed building. The foreman has to send and receive
accurate messages, at the right time, and to the right people, otherwise
the building will end up with structural flaws, and will probably fall
down again. Imagine if he simply threw the blueprints in the air, and
allowed the workers to pick up a piece each and act on what it said -
complete chaos! In the same way macrophages co-ordinate a complex
interplay between themselves and fibroblasts/satellite cells.
This is where PRP has the potential to fall down. PRP has variable
and inconsistent content and concentration. [9] There is no consensus on
timing of injection. What does a random bolus injection into an injury
achieve? Are we sending these effector cells a clear and co-ordinated set
of instructions with PRP? Or are they being sent a completely confusing
message? It would seem hopelessly optimistic and na?ve to presume that we
are accurately reproducing biological complexity.
PRP has shown promise in promoting accelerated scar tissue formation
in dental grafts [10] and wound healing [11], where regeneration of complex
tissue is not a goal. In Sports Medicine however, we require restoration
of functional tissue - contractile muscle or tendon of high tensile
strength - tissue of much greater complexity. The successes in maxillo-
facial applications are perhaps not analogous to these situations.
Whether or not PRP is eventually proven or disproven in Sports
Injuries, it is nevertheless a good start. The Sports Medicine world has
woken to the possibilities of regenerative medicine, and is trying to be
scientific in the development of novel therapies. In the future we will
have improved understanding of how the complex and overlapping processes
of tissue regeneration [12] are controlled by co-ordinating cells, stem
cells, effector cells and the messenger molecules that they employ, and
more importantly, how to manipulate these processes for a beneficial
effect.
References
1. de Vos RA, Weir A, van Schie HTM et al. Platelet-Rich Plasma
injection for Chronic Achilles Tendinopathy JAMA 2010;303(2):144-149
2. Anitua E, Andia I, Ardanza B, et al. Autologous platelets as a
source of proteins for healing and tissue regeneration. Thromb Haemost
2004;91:4-15.
3. Toumi H, F'guyer S, Best T. The role of neutrophils in injury and
repair following muscle stretch. J Anat 2006;208:459-470
4. Chazaud B, Brigitte M, Yacoub-Youssef H et al. Dual and beneficial
roles of macrophages during skeletal muscle regeneration. Exerc Sport Sci
Rev 2009;37(1):18-22
5. Jarvinen TAH, Jarvinen TLN, Kaariainen M. Muscle injuries: Biology
and Treatment. AJSM 2005;33:745-764
6. Li Y, Foster W, Deasy BM. Transforming growth factor-?1 induces
the differentiation of myogenic cells into fibrotic cells in injured
skeletal muscle. Am J Path 2004;164(3):1007-1019
7. Shen W, Li Y, Tang Y. NS-398, a Cyclooxygenase-2-specific
inhibitor, delays skeletal muscle healing by decreasing regeneration and
promoting fibrosis. Am J Path 2005;167(4):1105-1117
8. Bischoff R. Chemotaxis of Skeletal muscle satellite cells. Dev Dyn
1997;208:505-515
9. Creaney L, Hamilton B. Growth factor delivery methods in the
management of sports injuries: the state of play. BJSM 2008;42:314-320
10. Marx RE. Platelet-rich plasma: evidence to support its use. J
Oral Maxillofac Surg 2004;62(8):1047-8
11. Lacci KM, Dardik A. Platelet-rich plasma:support for its use in
wound healing. Yale J Biol Med 2010;83(1):1-9
12. Gates CB, Karthikeyan T, Fu F, Huard J. Regenerative Medicine for
the musculoskeletal system based on muscle-derived stem cell. J Am Acad
Orthop Surg 2008;16:68-76
Julien S Baker (1), Duncan S Buchan (2), Robert M Malina (3), Non E. Thomas (4)
1. University of the West of Scotland,
2. The University of Texas at Austin
3. Swansea University
Dear Editor,
We read with interest the recent statement released by BASEM on 26th November 2010 which criticises the way physical education (PE) is being taught in the United Kingdom. Previous authors suggest that...
Julien S Baker (1), Duncan S Buchan (2), Robert M Malina (3), Non E. Thomas (4)
1. University of the West of Scotland,
2. The University of Texas at Austin
3. Swansea University
Dear Editor,
We read with interest the recent statement released by BASEM on 26th November 2010 which criticises the way physical education (PE) is being taught in the United Kingdom. Previous authors suggest that youth spend less than 50% of PE time in moderate intensity activity and thus fail to procure health related benefits [1,2]. Interestingly, a recent investigation demonstrated a positive role for brief, interval training as a means of improving the health status of obese and overweight adolescents with unfavourable cardiometabolic profiles [3]. With this in mind we successfully developed and implemented a novel 7 week exercise intervention which aimed to determine the effects of PA programmes of different intensities and duration on three components of physical fitness, namely: cardiorespiratory fitness, muscular fitness and speed/agility [4]. Full details of the protocol can be found elsewhere [5,6].
Briefly, a cohort of adolescent school youth (N = 47 boys and 10 girls, 16.4 +/- 0.7 years of age) volunteered to participate in the study. Ethical approval was received from the University of the West of Scotland Ethics committee. Maturation status was obtained prior to experimental data collection. Participants were recruited from two PE classes in years 5 and 6. Year 5 pupils acted as the control group whereas year 6 pupils were randomly assigned to a high intensity training group (HIT) or a moderate (MOD) intensity group. Participants in the HIT group (15 boys, 2 girls) were required to complete a 30 s maximal effort sprint within a 20 m distance separated by cones. Participants were instructed to sprint from the midpoint to the first marker, turn, and then sprint 20 m in the opposite direction to the second marker. Participants repeated the protocol four times with a 30 s recovery period between sprints. This equated to 2 mins of maximal effort sprinting interspersed with 2 min recovery. The protocol was performed 3 times weekly. Training progression was implemented by increasing the number of repetitions from four during weeks 1 and 2, to five during weeks 3 and 4, to six during weeks 5 and 6. During week 7, participants still performed six repetitions but each was interspersed by only 20 s recovery.
Participants in the MOD group (12 boys and 4 girls) were instructed to exercise at a moderate intensity of 70% VO2max as utilized in other studies [6], by running steadily for a period of 20 mins. The speed of exercise was determined by each participants performance in the 20 metre multistage fitness test (MSFT). Participants were instructed to keep pace with a CD that emitted a continuous audio signal for a period of 20 min. All participants had indices of obesity and blood pressure recorded in addition to four physical performance measures pre and post intervention. These included the 20 MSFT, the counter movement jump (CMJ), agility and the 10m sprint test.
Overall, it was apparent that specific physiological adaptations occurred relative to the stimulus provided. Participants in the MOD group experienced a 26.8% improvement in 20 MSFT and a 7.3% improvement in CMJ performance. Participants in the HIT group experienced an 8.3% and a 5.1% improvement in both the 20 MSFT and CMJ. Participants in the HIT group also experienced a 1.5% and 5% improvement in 10-m sprint and 505-agility performance though no improvements were noted in the MOD group. Though the participants in both groups experienced improvements, it should be noted that these improvements in the HIT group occurred in 85% less exercise time compared to that of the MOD group. Participants in the HIT group also experienced a significant reduction in systolic blood pressure SBP post-intervention (112 +/- 10 vs. 106 +/- 11 mm Hg) (P=0.017). Thus, significant improvements in physical fitness were found in both groups after exercising for only seven weeks (3 times per week).
Despite overwhelming evidence supporting the health benefits of regular PA, many youth fail to meet minimal recommendations. This study has demonstrated that HIT is a time efficient means of improving components of health in youth. Given the time constraints of school curricula, incorporating a HIT protocol into the PE curriculum may function to improve PA levels and health status of adolescents. Further research investigating the effects of HIT on markers of health status in youth seems recommended.
References
1. Nettlefold, L., McKay, H. A., Warburton, D. E., McGuire, K. A., Bredin, S. S., & Naylor, P. J. (2010). The challenge of low physical activity during the school day: at recess, lunch and in physical education. Br J Sports Med. doi: bjsm.2009.068072 [pii] 10.1136/bjsm.2009.068072
2. Fairclough SJ, Stratton G (2006) A review of physical activity levels during elementary school physical education. J Teach Phys Educ 25: 239-257
3. Tjonna AE, Stolen TO, Bye A, Volden M, Slordahl SA, Odegard R, Skogvoll E, Wisloff U (2009) Aerobic interval training reduces cardiovascular risk factors more than a multitreatment approach in overweight adolescents. Clin Sci 116: 317-326
4. Ortega FB, Ruiz JR, Castillo MJ, Sjostrom M (2008) Physical fitness in childhood and adolescence: a powerful marker of health. Int J Obes 32: 1-11
5. Buchan, D. S., Ollis, S., Thomas, N. E., & Baker, J. S. (2010). The influence of a high intensity physical activity intervention on a selection of health related outcomes: an ecological approach. BMC Public Health, 10(1), 8.
6. Buchan, D.S. Ollis, S. Thomas, N.E. Cooper, S.M. Malina, R.M and Baker, J.S. Physical Activity Interventions: Effects of Duration and Intensity. Scand J Med Sci Spor (Under Review).
7. Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K (1996) Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc 28: 1327-1330
We agree with Ian Shrier that the finding of an effect of stretching
on risk of muscle, ligament and tendon injuries should be interpreted with
caution. That is why we wrote "The finding of an effect of stretching on
muscle, ligament and tendon injury risk needs to be considered cautiously
because muscle, ligament and tendon injury risk was a secondary outcome,
and there was no evidence of an effect of stretching on the p...
We agree with Ian Shrier that the finding of an effect of stretching
on risk of muscle, ligament and tendon injuries should be interpreted with
caution. That is why we wrote "The finding of an effect of stretching on
muscle, ligament and tendon injury risk needs to be considered cautiously
because muscle, ligament and tendon injury risk was a secondary outcome,
and there was no evidence of an effect of stretching on the primary
outcome of all-injury risk. If stretching had reduced the risk of muscle,
ligament and tendon injuries without increasing the risk of other
injuries, we would expect a reduction in all-injury risk." Nonetheless,
after a prolonged discussion of this issue we decided that the finding
could not be totally dismissed. We believe that it was appropriate to
report the observed effect on muscle, ligament and tendon injuries with an
explicit acknowledgement of the uncertainty associated with this finding.
Regardless of whether one accepts the finding that stretching reduces
risk of muscle, tendon and ligament injuries, the implications would
appear to be the same. Even if the effect is real, it is quite small in
absolute terms (even in this population, at quite a high risk of injury,
only "one injury to muscle, ligament or tendon was prevented for every 20
people who stretched for 12 weeks"). For this reason the data from this
study do not appear to provide support for the practice of stretching, at
least in so far as the aim is to reduce injury risk. The stronger
justification for stretching, though still a marginal one in our view, is
provided by the clear evidence of a very small effect of stretching on
soreness. For other outcomes, such as performance or range of motion our
study did not provide any data.
It is not yet known whether stretching is best carried out before
exercise, after exercise, or both before and after exercise. We were
surprised, when planning this study, to learn that most Australian stretch
before exercise but not after, and most Norwegians stretch after exercise
but not before! It was for that reason we designed a trial in which
participants stretched both before and after exercise. We do not agree
with Ian Shrier's suggestion to conduct an unplanned post-hoc comparison
of the non-randomised subgroups that chose to stretch only before, only
after, or both before and after exercise. Such an analysis would almost
certainly be seriously confounded and would probably be uninterpretable;
at any rate it hardly seems consistent with his disapproval of our much
more disciplined pre-planned secondary comparison between randomised
groups. The only truly satisfactory way to resolve the issue of whether it
is better to stretch before or after exercise is to conduct a further
randomised trial in which participants are randomised to those two
conditions.
I recently read the article Jamtvedt et al on whether pre and post
stretching prevents injury 1 with interest. I commend the authors for
their well-conducted study and would like to comment on two particular
issues.
First, the authors correctly point out that there was no difference in the
primary outcome of all injuries, and that the analysis showing an absolute
22% reduction in muscle, ligament a...
I recently read the article Jamtvedt et al on whether pre and post
stretching prevents injury 1 with interest. I commend the authors for
their well-conducted study and would like to comment on two particular
issues.
First, the authors correctly point out that there was no difference in the
primary outcome of all injuries, and that the analysis showing an absolute
22% reduction in muscle, ligament and tendon injuries with stretching
should be interpreted cautiously. However, they then continue to say
"Nonetheless, it is plausible that stretching reduces muscle, ligament and
tendon injuries, and it may be implausible that stretching increases other
injuries". Moreover, in the conclusion, they only mention the "probable
reduction in muscle, ligament and tendon injuries" and omit the absence of
an effect on the primary outcome of overall injuries. This type of
thinking appears to be gaining popularity. For example, Small et al (cited
by the current article) emphasized the decrease in musculo-tendinous
injuries they observed in their review of stretching and discounted the
associated increase in stress fractures and "shin splints" 2.
In other areas of medicine, we have already learned the difficult lesson
that "all-cause mortality" is generally a much more important outcome
compared to "disease-specific mortality" because interventions can cause
damage through unrecognized mechanisms. It would be a pity if the sport
medicine world has to go through the same lessons. Plausible reasons why
stretching would increase some types of injuries are already available
from a review of basic science evidence 3. Because Jamtvedt et al do not
actually detail the non muscle-tendon-ligament injuries, I will use the
example from Small et al. related to stress fractures and "shin splints"
(not defined, but presumably periostitis and compartment syndrome). An
acute bout of stretching causes weakness, 4 which is expected to lead to
1) an increased force transmission to the bone 5, 6, which would lead to
increased stress reaction and stress fractures and 2) a possible increase
in compensatory muscle use, which could theoretically cause shin splints
of any cause. Further, stretching-induced weakness would theoretically
also decrease proprioception, although this remains to be studied. Authors
who decide to report sub-group analyses need to show the same analyses for
all the sub-groups created by the categorization.
Second, "stretching" as an intervention is intricately related to the
timing of the stretch, and one expects different results from stretching
before exercise compared to stretching at other times 7. In their
conclusion, Jamtvedt et al suggest that "the results of this trial support
the decision to stretch" 1, with no mention of the timing; reviews by
Small et al 2, and Thacker et al 8 (cited by the current article) made the
same error. In brief, the effects of "stretching" are similar to those of
"weight lifting". An acute bout of weight lifting or stretching will cause
an immediate decrease in strength, power and endurance 4. However, if one
weight lifts or stretches for weeks, there is an increase in strength,
power and endurance 4. Based on this, one would expect that stretching
before every exercise session would increase the risk of injury due the
acute effects, but there would also be an expected decrease in injury risk
as the body adapts and strengthens over time. If the two effects were
relatively balanced, one would expect no effect on overall injury rate.
However, if one stretched regularly but not before exercise, then one
would expect only the benefits, with a decrease in overall injury rate.
Indeed, there have been three randomized trials prior to this study and a
meta-analysis of these (one study had subjects stretch before and after
exercise as in the current study 9) suggests regular stretching not before
exercise reduces injury risk [OR=0.68 (95%CI: 0.52, 0.88)] 7.
Given these previous studies, it would be interesting for the authors to
conduct a post-hoc analysis (with the appropriate cautious interpretation)
comparing the injury risk among those who stretched only before exercise,
those that stretched only after exercise, and those that stretched both
before and after exercise.
In summary, there should be little controversy about 1) post-exercise
stretching reducing acute muscle soreness, just as it reduces any chronic
musculoskeletal pain 10, presumably due to its well-studied effects on
stretch-tolerance (a form of analgesia) 11, 12, and 2) stretching not
before exercise reducing injury risk given that both basic science and
clinical science provide consistent evidence, although a couple more
confirmatory studies could be helpful. Future research priorities should
focus on questions where there is little to no evidence such as 1) whether
post-exercise stretching is as beneficial as stretching at other times, 2)
what are the effects for high intensity sports, 3) the effects of
stretching on rehabilitation of injuries, and 4) the effects on the
performance in injured athletes (all published studies examined healthy
subjects) 13.
Ian Shrier MD, PhD, Dip Sport Med, FACSM
Centre for Clinical Epidemiology and Community Studies
SMBD-Jewish General Hospital
3755 Cote Ste-Catherine Rd
Montreal, Qc H3T 1E2
Tel: 514-340-7563
Fax: 514-340-7564
References
1. Jamtvedt G, Herbert RD, Flottorp S, et al. A pragmatic randomised
trial of stretching before and after physical activity to prevent injury
and soreness. Br J Sports Med. 2010;44:1002-1009.
2. Small K, McNaughton L, Matthews M. A systematic review into the
efficacy of static stretching as part of a warm-up for the prevention of
exercise-related injury. Res Sports Med. 2008;16:213-231.
3. Shrier I. Does stretching help prevent injuries? In: MacAuley D, Best
T, eds. Evidence-based sports medicine. London: BMJ Publishing Group;
2007.
4. Shrier I. Does stretching improve performance: A systematic and
critical review of the literature. Clin J Sport Med. 2004;14:267-273.
5. Mizrahi J, Verbitsky O, Isakov E. Fatigue-related loading imbalance on
the shank in running: a possible factor in stress fractures. Ann Biomed
Eng. 2000;28:463-469.
6. Christina KA, White SC, Gilchrist LA. Effect of localized muscle
fatigue on vertical ground reaction forces and ankle joint motion during
running. Hum Mov Sci. 2001;20:257-276.
7. Shrier I. Meta-analysis on preexercise stretching. Med Sci Sports
Exerc. 2004;36:1832-1832.
8. Thacker SB, Gilchrist J, Stroup DF, et al. The impact of stretching on
sports injury risk: a systematic review of the literature. Med Sci Sports
Exerc. 2004;36:371-378.
9. Amako M, Oda T, Masuoka K, et al. Effect of static stretching on
prevention of injuries for military recruits. Mil Med. 2003;168:442-446.
10. Law RY, Harvey LA, Nicholas MK, et al. Stretch exercises increase
tolerance to stretch in patients with chronic musculoskeletal pain: a
randomized controlled trial. Phys Ther. 2009;89:1016-1026.
11. Magnusson SP, Simonsen EB, Aagaard P, et al. Mechanical and
physiological responses to stretching with and without preisometric
contraction in human skeletal muscle. Arch Phys Med Rehabil. 1996;77:373-
378.
12. Halbertsma JPK, Mulder I, Goeken LNH, et al. Repeated passive
stretching: acute effect on the passive muscle moment and extensibility of
short hamstrings. Arch Phys Med Rehabil. 1999;80:407-414.
13. Shrier I. Stretching perspectives. Curr Sports Med Rep. 2005;4:237-
238.
In response to the editorial- Physical activity in the UK: a unique
crossroad.Br J Sports Med 2010 vol44 no 13
I was delighted to read Dr Weilers editorial which eloquently
presents many of the issues currently faced in exercise medicine.
It is so important to debate this subject-particularly as we are in a
unique position in the U.K to effect permanent change.
I was interested in Dr Weilers' view that the intro...
In response to the editorial- Physical activity in the UK: a unique
crossroad.Br J Sports Med 2010 vol44 no 13
I was delighted to read Dr Weilers editorial which eloquently
presents many of the issues currently faced in exercise medicine.
It is so important to debate this subject-particularly as we are in a
unique position in the U.K to effect permanent change.
I was interested in Dr Weilers' view that the introduction of the GGPAQ
into QOF would be a valuable place to start what will have to be a process
of cultural change. I would like to debate this opinion further.
It has been clearly established in the literature that changes in physical
activity levels in the long term are not easy to effect. The most
successful interventions involve patient centred, long term, well
supported, behaviourally based interventions delivered by highly motivated
and well trained medical professionals. I do not agree with your statement
that 'brief interventions (3-10min) can lead to substantial increases in
physical activity level (by around 30%)'. I am not aware of any evidence
to substantiate this claim, particularly in the long term. The studies
which have shown these sorts of results have used of a much more intense
intervention, not sustainable within the NHS, and most do not show
significant long term results (greater than 3 months).(1,2)
I agree that physical activity promotion to 'healthy' populations can only
be delivered by primary care. I feel, however, that we are not yet ready
for GGPAQ. The effect of creating another 'box to tick' in an already
target driven culture, I feel, at this stage would be counterproductive.
We have a long way to go in the process of educating G.P's and practice
nurses about the evidence base for the benefits of and the delivery of
exercise prescription. It will, rightly, take convincing evidence of
effectiveness to persuade G.P's to engage in this process. There is,
currently, no evidence that could possibly lead us to suppose that the
introduction of GGPAQ would lead to significant and sustained changes in
physical activity levels
?1million , to introduce a QOF point does not seem an enormous amount of
money until you consider that with that sum, per year, you could employ 10
SEM consultants. I feel this would be a very much more effective way of
spending the limited resources available at this stage. A single SEM
consultant could provide a comprehensive education programme from medical
school to primary and secondary care, could lead good quality,
translational research into cost effective ways of delivering exercise
interventions and could coordinate existing services for exercise in
chronic disease which are often non-existent or ineffective and poorly
evaluated. They could assess local needs, building on strengths of
existing structures and working on the weaknesses. They could improve
links with the fitness industry which in many cases are poorly supported
and therefore less effective.
I agree, clinical research is essential at this stage and funding is not
easy to come by. The N.H.S needs to address this through its own research
organisations. Partnerships with the tremendously powerful fitness
industry may also help to fund translational research as might charitable
foundations for chronic disease research.
Overall, I agree with much of the editorial, but feel that in the current
economic climate , we need to think very carefully before rolling out
blanket schemes which are open to criticism from the very people we are
hoping will deliver them.
1.Eakin EG, Glasgow RE, Riley KM. Review of primary care-based
physical activity intervention studies: effectiveness and implications for
practice and future research. J Fam Pract. 2000; 49: 158-168.
2. Lawlor D.A The Effect of physical activity advice given in primary care
consultations-a review. Journal of public Health Medicine.2001; 23:219-226
An article entitled "The challenge of low physical activity during
the school day: at recess, lunch and in physical education" was recently
published in the British Journal of Sport Medicine.[1] Briefly, Nettlefold
and colleagues used uniaxial accelerometers (Actigraph GT1M) to estimate
the level of physical activity (PA) over the school day in Canadian
children aged 8-11 years. One of their most striking findings was th...
An article entitled "The challenge of low physical activity during
the school day: at recess, lunch and in physical education" was recently
published in the British Journal of Sport Medicine.[1] Briefly, Nettlefold
and colleagues used uniaxial accelerometers (Actigraph GT1M) to estimate
the level of physical activity (PA) over the school day in Canadian
children aged 8-11 years. One of their most striking findings was that
only 1.8% of girls and 2.9% of boys in the compliant fraction (216 of 629
students recruited) met the U.S. guideline of performing moderate to
vigorous physical activity (MVPA) during at least 50% of their physical
education (PE) classes.[2] This troubling finding has important
implications regarding the quality of PE programmes.
All the PE classes in this study were taught by regular classroom
teachers, as it is commonly the case for primary students in British
Columbia and elsewhere.[1, 3] However, in interview data collected from
two different Manitoban primary schools, DeCorby and colleagues [4] found
normal classroom teachers were very uncomfortable in delivering PE
instruction, due to a lack of specific knowledge and appropriate training.
The principal of the school concerned commented: "I really feel sorry for
them [the kids] because we wouldn't ask teachers to teach music, for
example, with no training, but yet we do with phys. ed."[4] In the second
school that was examined, PE was taught by a specialist who developed a
programme that focused on the acquisition of developmentally appropriate
motor skills, a variety of physical activities performed in a non-
competitive environment, and positive social development. That programme
proved successful in stimulating participation and enjoyment, particularly
among the girls and the boys who had difficulty in undertaking PE.[4]
A small number of experimental, quasi-experimental and/or
longitudinal studies in various jurisdictions have compared the response
of primary school students to high quality, specialist taught PE
programmes with the response to a "normal" curriculum. In the Trois-
Rivieres study, conducted from 1971 to 1978, 546 Quebecois children were
assigned (on the basis of year of entry to a school) to either an
experimental programme (5 h of PE per week taught by a qualified physical
educator from Grades 1 through 6) or the standard curriculum (40 min of PE
once per week under the supervision of their home-room teacher).[5] The PE
classes for children in the experimental group were designed to ensure
that students spent most of the class performing vigorous exercise (heart
rate equal or greater than 160 beats per minute), and this was verified by
telemetry. Moreover, questionnaire data demonstrated that there was not a
compensatory reduction of PA level during the rest of the day.[5]
The CATCH intervention studied American children in grades 3 to 5;
the experimental group received a comprehensive intervention which
included modifications to school food services, enhanced PE classes and
use of health curricula in the classroom [6]. The proportion of MVPA
during PE for the experimental group gradually increased to over 50% of
class time; they also accumulated more intense PA than the controls (58.6
vs. 46.5 minutes daily).[6] Similarly, in the SPARK project, American
children who received PE from a specialist accumulated more minutes of
MVPA during their PE classes than those who were taught by a partially
trained or an untrained (e.g. control) classroom teacher (40 vs. 33 vs. 18
minutes respectively).[7]
More recently, a Swiss study of students in Grades 1 and 5 has
examined the effects of supplementing the regular PE curriculum (3 weekly
45 minutes PE lessons taught by a classroom teacher) by twice weekly 45
minutes specialist-taught PE lessons, several 5 minutes PA breaks
throughout the school day, and 10 minutes of daily PA homework in the
context of a cluster randomized control trial.[8] Accelerometry data
suggested that students in the experimental group accumulated more MVPA
and total PA than controls during school time, but unfortunately in this
study there was a compensatory reduction of PA during leisure hours, so
that the experimental group did not increase their total activity for the
day relative to controls.
Some investigators have noted quite strong relationships between
curricular time devoted to PE and health-related outcomes including: a
higher maximal aerobic power and muscular fitness, enhanced motor skills,
a reduction of adiposity, and enhanced academic achievement.[3, 7-9]
German researchers compared sixth grade children who were assigned to an
enhanced PE program for an entire school year (45 minutes of daily PE with
a particular emphasis on endurance training) to a control group which
received 45 minutes sessions of PE only twice per week.[10] ANCOVA
analyses revealed major increases in maximal aerobic power (a gain of 3.7
ml*kg-1*min-1) and circulating progenitor cells and a trend to a decrease
in the prevalence of overweight and obesity (from 12.8% to 7.3%, N.S.) in
the experimental group.[10]
These several investigations highlight the importance of specialist
PE training to the quality of PE programmes, and their resulting ability
to maximize the fraction of class time spent in MVPA. Key elements of a
quality programme include: 1) development of a full range of motor skills
during early primary school; 2) improvement of both aerobic and muscular
fitness through a wide variety of physical activities; 3) a reduced
emphasis on competition, in order to foster participation of less skilled
individuals, and 4) the development of skills that will encourage physical
activity throughout the individual's lifespan.[3, 4, 8] Nevertheless, the
age-related decline in PA points the need for further research on long
term outcomes.[3] Changes in the content of PE classes still seem needed
to encourage long term participation in a volume of physical activity that
is optimal for health.
The British Columbia PE curriculum specifies a wide range of learning
outcomes, from knowledge of the topic to active living, movement skills,
safety, fair play and leadership.[1] Possibly, the demands on the PE class
are too diverse, and the responsibility for teaching some of these topics
should be delegated to other school disciplines. This strategy was
effective in the CATCH intervention.[6]
REFERENCES
1. Nettlefold L, McKay HA, Warburton DER, et al. The challenge of low
physical activity during the school day: at recess, lunch and physical
education. Br J Sport Med. Published Online First 9 March 2010. doi:
10.1136/bjsm.2009.068072
2. United States Department of Health and Human Services. Healthy
people 2010: understanding and improving health. Washington, DC: U.S.
Government Printing Office 2000.
3. Trudeau F, Shephard RJ. Contribution of school programmes to
physical activity levels and attitudes in children and adults. Sports Med
2005;35(2):89-105.
4. DeCorby K, Halas J, Dixon S, et al. Classroom teachers and the
challenge of delivering quality physical education. J Educ Res
2005;98(4):208-220.
5. Lavallee H, Shephard RJ, Jequier J-C, et al. A compulsory physical
activity program and out-of-school free activities in the Trois-Rivieres
study [In French]. In: Lavallee H, Shephard RJ, eds. Child growth and
development. Trois-Rivieres, Qc: editions du Bien Public 1982:61-71.
6. Luepker RV, Perry CL, McKinlay SJ, et al. Outcomes of a field
trial to improve children's dietary patterns and physical activity: the
Child and Adolescent Trial for Cardiovascular Health (CATCH). JAMA
1996;275(10):768-776.
7. Sallis JF, McKenzie TL, Alcaraz JE, et al. The effect of a 2-year
physical education program (SPARK) on physical activity and fitness in
elementary school students. Am J Public Health 1997;87(8):1328-1334.
8. Kriemler S, Zahner L, Schindler C, et al. Effect of school based
physical activity programme (KISS) on fitness and adiposity in primary
schoolchildren: cluster randomized control trial. BMJ 2010;340:c785.
doi:10.1136/bmj.c785
9. Shephard RJ. Long-term studies of physical activity in children -
The Trois-Rivieres experience. In: Binkhorst RA, Kemper HCG, Saris WHM,
eds. Children and Exercise XI. Champaign, Ill.: Human Kinetics 1985:252-
259.
10. Walther C, Gaede L, Adams V, et al. Effect of increased exercise
in school children on physical fitness and endothelial progenitor cells: A
prospective randomized trial. Circulation 2009;120:2251-2259.
Dear Editor,
Figure 2, which is critical to the findings of this publication, presents an intra-individual group relationship; laboratory studies regarding the influence of dehydration on exercise performance utilize an individual as his/her own control. The cross-sectional trend in Figure 2, which arose from a single field study, should not be equated with a randomized, controlled, repeated measures experimental desig...
Dear Editor,
Please check www.ligmaster.com for info on an ankle, knee, elbow and shoulder non-radiographic arthrometer that quantitatively determines the percentage tear in all of the clinically important ligament of the above joints.
I am afraid a little disappointed with this review. I take issue with the premise that osteitis pubis and osteomyelitis could possibly be considered in the same review. As correctly identified in the piece, one is acute and one chronic with different predisposing and underlying pathology. Further more, although the relevance of Level 4 evidence is challenged, there is little comment on either the diagnostic criteria, the...
I fully agree with the comment from Dr Creaney regarding PRP. Unfortunately, there is little sound clinical science supporting the use at the moment. The design of studies published so far has been far from perfect. The studies with poor design have tended to produce good results, whereas the RCTs with proper design have shown less of an effect. Another challenge is the multitude of unknown clinical variables such as amou...
Dear Sir,
I congratulate the IOC Consensus panel on having produced as clear a summary of the current understanding of the basic and clinical science relating to PRP as the body of published literature allows. While there was initially great hope in Sport Medicine circles that PRP would become the magic bullet for injuries, recent trials such as de Vos [1], have failed to provide that conclusive evidence so de...
Julien S Baker (1), Duncan S Buchan (2), Robert M Malina (3), Non E. Thomas (4)
1. University of the West of Scotland,
2. The University of Texas at Austin
3. Swansea University
Dear Editor,
We read with interest the recent statement released by BASEM on 26th November 2010 which criticises the way physical education (PE) is being taught in the United Kingdom. Previous authors suggest that...
We agree with Ian Shrier that the finding of an effect of stretching on risk of muscle, ligament and tendon injuries should be interpreted with caution. That is why we wrote "The finding of an effect of stretching on muscle, ligament and tendon injury risk needs to be considered cautiously because muscle, ligament and tendon injury risk was a secondary outcome, and there was no evidence of an effect of stretching on the p...
Editor,
I recently read the article Jamtvedt et al on whether pre and post stretching prevents injury 1 with interest. I commend the authors for their well-conducted study and would like to comment on two particular issues.
First, the authors correctly point out that there was no difference in the primary outcome of all injuries, and that the analysis showing an absolute 22% reduction in muscle, ligament a...
In response to the editorial- Physical activity in the UK: a unique crossroad.Br J Sports Med 2010 vol44 no 13
I was delighted to read Dr Weilers editorial which eloquently presents many of the issues currently faced in exercise medicine. It is so important to debate this subject-particularly as we are in a unique position in the U.K to effect permanent change. I was interested in Dr Weilers' view that the intro...
An article entitled "The challenge of low physical activity during the school day: at recess, lunch and in physical education" was recently published in the British Journal of Sport Medicine.[1] Briefly, Nettlefold and colleagues used uniaxial accelerometers (Actigraph GT1M) to estimate the level of physical activity (PA) over the school day in Canadian children aged 8-11 years. One of their most striking findings was th...
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