To systematically review the current literature that relates the effects of age and skill level to motor control patterns of knee musculature co-contraction during functional movements.
A search of electronic databases was performed with the search terms specifying co-contraction (cocontract*, co-contract*, coactive* or co-activ*). The search was focused on the effects age and/or skill level and were limited by the keywords of age or skill level (skill*) or experience (experi*).
The search yielded a total of six peer-reviewed manuscripts that met the search criteria and were included in the review.
The relationship between adequate dynamic joint stability and efficient movement patterns are complex. Co-contraction related to age and skill development varies among studies due to technical and practical considerations. Adequate antagonistic co-contraction of hamstring musculature seems to be a component of all functional movements, possibly maintain dynamic knee stability and protect against excessive joint loads. Future investigations that further delineate the appropriate lower extremity agonist and antagonist relationships during dynamic tasks may help elucidate injury risk mechanisms in specific populations.
A recent editorial in Medicine and Science in Sports and Exercise concludes that the study of Hawkins and colleagues confirms "beyond any doubt the proposition of Hill and Lupton". It is not clear which of Hill and Lupton’s propositions have been proved "beyond any doubt".
A review of all the relevant publications of A V Hill and his colleagues.
Hill and Lupton believed (i) that myocardial ischaemia limits maximal exercise performance by inducing circulatory failure; (ii) that a "governor" protects the ischaemic heart by causing a "slowing of the circulation" during maximal exercise; (iii) that the oxygen cost of running increases exponentially at speeds above 16 km per hour; and (iv) that humans reach their highest measurable oxygen consumption of about 4 litres per minute at that running speed. Hill and Lupton neither invented the concept of the "plateau phenomenon" nor utilised this concept to establish that a "true" maximum oxygen consumption (VO2max) had been achieved. Nor did they measure cardiac output during exercise.
Accepting uncritically this modern interpretation of Hill and Lupton’s theory that the cardiac output limits maximal exercise performance whether or not the plateau phenomenon is present fails to answer the question first posed more than 20 years ago: What causes the termination of exercise when the "true" VO2max is achieved without the "plateau phenomenon"? According to the Hill and Lupton model, this cannot be because a limiting cardiac output has been reached. Since a majority of maximal exercise tests terminate in the absence of the "plateau phenomenon", this is seemingly an important question.
The diagnosis of muscular lesions suffered by athletes is usually made by clinical criteria combined with imaging of the lesion (ultrasonography and/or magnetic resonance) and blood tests to detect the presence of non-specific muscle markers. This study was undertaken to evaluate injury to fast and slow-twitch fibres using specific muscle markers for these fibres.
Blood samples were obtained from 51 non-sports people and 38 sportsmen with skeletal muscle injury. Western blood analysis was performed to determine fast and slow myosin and creatine kinase (CK) levels. Skeletal muscle damage was diagnosed by physical examination, ultrasonography and magnetic resonance and biochemical markers.
The imaging tests were found to be excellent for detecting and confirming grade II and III lesions. However, grade I lesions were often unconfirmed by these techniques. Grade I lesions have higher levels of fast myosin than slow myosin with a very small increase in CK levels. Grade II and III lesions have high values of both fast and slow myosin.
The evaluation of fast and slow myosin in the blood 48 h after the lesion occurs is a useful aid for the detection of type I lesions in particular, since fast myosin is an exclusive skeletal muscle marker. The correct diagnosis of grade I lesions can prevent progression of the injury in athletes undergoing continual training sessions and competitions, thus aiding sports physicians in their decision making.
Large inter-subject variability in responses to eccentric exercise has been reported. This study investigated the hypothesis that the variability of changes in indirect markers of exercise-induced muscle damage (EIMD) would be explained by work performed and/or torque generated during eccentric exercise.
Subjects (n = 53) performed 60 maximal eccentric actions of the elbow flexors on an isokinetic dynamometer that forcibly extended the elbow joint from 60° to 180° at a constant velocity (90° s–1). Markers of EIMD included maximal voluntary isometric contraction torque at 90° elbow flexion (MVC), range of motion, plasma creatine kinase activity and muscle soreness. Measurements were taken 2 days before, immediately after and 1–4 days post-exercise. Pearson’s correlation coefficient was used to examine relationships between exercise parameters (total work, change in total work, torque produced during exercise, change in peak torque) and markers of EIMD.
Large inter-subject variability was evident for both work and torque during exercise, and changes in all markers of EIMD. Contrary to the hypothesis, total work (normalised for individual pre-exercise MVC) did not correlate significantly with any markers of EIMD, with the exception of MVC (r = 0.3). Total work performed and changes in total work showed higher correlations with some markers, but no r-values exceeded 0.4. Normalised exercise torque and the changes in peak torque during exercise were not correlated with changes in MVC, or other markers.
These results suggest the large inter-subject variability in responses to eccentric exercise is not associated with work performed or torque generated during eccentric exercise.
To compare the energy expenditure of adolescents when playing sedentary and new generation active computer games.
Cross sectional comparison of four computer games. Setting Research laboratories.
Six boys and five girls aged 13–15 years.
Participants were fitted with a monitoring device validated to predict energy expenditure. They played four computer games for 15 minutes each. One of the games was sedentary (XBOX 360) and the other three were active (Wii Sports).
Predicted energy expenditure, compared using repeated measures analysis of variance.
Mean (standard deviation) predicted energy expenditure when playing Wii Sports bowling (190.6 (22.2) kl/kg/min), tennis (202.5 (31.5) kl/kg/min), and boxing (198.1 (33.9) kl/kg/min) was significantly greater than when playing sedentary games (125.5 (13.7) kl/kg/min) (P<0.001). Predicted energy expenditure was at least 65.1 (95% confidence interval 47.3 to 82.9) kl/kg/min greater when playing active rather than sedentary games.
Playing new generation active computer games uses significantly more energy than playing sedentary computer games but not as much energy as playing the sport itself. The energy used when playing active Wii Sports games was not of high enough intensity to contribute towards the recommended daily amount of exercise in children.
To establish injury profile of collegiate rugby union in the USA
31 men’s and 38 women’s collegiate rugby union teams prospectively recorded injuries during games and practice during the 2005–06 season. Three teams withdrew before data collection. An injury was defined as one: (1) occurring in an organised intercollegiate game or practice; and (2) requiring medical attention during or after the game or practice, or (3) resulting in any restriction of the athletes’ participation for >=1 day(s) beyond the day of injury, or in a dental injury.
In total, 847 injuries (447 in men; 400 in women) during 48 026 practice (24 280 in men; 23 746 in women) and 25 808 game (13 943 in men; 11 865 in women) exposures were recorded.
During games, injury rates of 22.5 (95% CI 20.2 to 25.0) and 22.7 (20.2 to 25.5) per 1000 game athletic exposures or 16.9 (15.1 to 18.9) and 17.1 (15.1 to 19.1) per 1000 player game hours were recorded for men and women, respectively. Over half of all match injuries were of major severity (>7 days’ absence) (men 56%; women 51%) and the tackle was the game event most often associated with injury (men 48%; women 53%).
Collegiate game injury rates for rugby were lower than rates recorded previously in men’s professional club and international rugby and lower than reported by the National Collegiate Athletic Association Injury Surveillance System for American football, but similar to rates reported for men’s and women’s soccer in 2005–06.
To identify the most common causes of death during sports activity in the population of Hamburg, Germany, and to identify which groups of sportspeople are particularly in danger of dying during sports and in which types of sport most fatalities occur.
We performed a 10-year autopsy-based retrospective study of all 48 335 fatalities in Hamburg and the surrounding areas that were subjected to police investigations between 1997 and 2006 and screened for sports-related deaths. The main outcome measure was cause of death depending on form of sport, age and risk factors.
Most of the fatalities were male. In natural deaths, cardiac causes were the most frequent causes found, with running and football being the most frequent forms of sport in which death had occurred. In some of the cases, sports medical examinations had been performed before death, certifying eligibility for the respective activity. Traumatic deaths were found in all age groups, with younger age groups more likely to have traumatic than natural deaths, and as expected, occurred more commonly in "risky" outdoor activities.
Although exercise can have beneficial effects on health, fatalities related to sports activity occur. Cardiac disease is the main cause of sudden death from natural causes. In patients with pre-existing coronary heart disease, left ventricular hypertrophy constitutes a risk factor for exercise-related sudden death. Traumatic deaths often happen on holiday outside the person’s country of dwelling, and are most commonly attributable to drowning and blunt trauma. Preparticipation medical screening cannot always prevent fatal incidents during sports activity. Postmortem macroscopic and histological examination can clarify the cause of death and legal issues.
To investigate whether adipose subcutaneous tissue or skeletal muscle mass decreased during a non-stop ultra-endurance triathlon.
Descriptive field study.
The Triple Iron Triathlon Germany 2006 in Lensahn: 11.6 km swimming, 540 km cycling and 126.6 km running.
17 male Caucasian triathletes, mean (SD) age 39.2 (7.5) years, height 178 (5) cm, body mass 80.7 (8.9) kg and body mass index (BMI) 25.4 (2.4) kg/m2.
None.
Determination of body mass, skin-fold thicknesses, limb circumference, skeletal muscle mass and percentage body fat in order to show changes after the race.
A significant decrease was shown for body mass (p<0.001), BMI (p<0.001) and calculated percentage body fat (p<0.001) whereas skeletal muscle mass did not change significantly (p>0.05). Circumferences of the thigh, upper arm and calf did not decrease significantly (p>0.05), whereas all skin-fold thicknesses decreased significantly (p<0.05), with the exception of those at the chest and thigh. A significant correlation was found between the loss of percentage body fat and the loss of body mass (p<0.01, r2 = 0.55) as well as change in percentage body fat with race performance (p<0.05, r2 = 0.24).
Ultra-endurance triathletes at the Triple Iron Triathlon Germany 2006 showed a significant decrease in body mass and percentage body fat, where decrease in percentage body fat was associated with race intensity.
The objective was to determine the effect of trunk focused neuromuscular training (TNMT) on hip and knee strength. The hypothesis was that TNMT would increase standing isokinetic hip abduction, but not knee flexion/extension, strength.
21 high-school female volleyball players (14 TMNT, mean age 15.4 (1.4) years, weight 170.5 (5.0) cm, height 64.1 (8.5) kg and 7 controls, mean age 16.0 (1.7) years, height 173.4 (10.0) cm, weight 63.9 (5.3) kg; p>0.05) were recruited to participate in this study. The 14 TNMT subjects participated in a TNMT protocol (twice weekly) over a 10 week period in addition to their standard once-weekly off-season strength training. Standing isokinetic hip abduction strength and seated knee flexion/extension strength were measured before and after TNMT.
A significant interaction of group and time was observed. The TNMT group increased isokinetic hip abduction strength approximately 15% (13.5% in the dominant leg: mean (SD) 46.6 (10.1) to 52.9 (11.4) foot-pounds and 17.1% in the non-dominant leg: 46.1 (10.4) to 54.0 (10.7) foot-pounds; p = 0.01). There was no difference in the control group in pre-test versus post-test measures. Post-test results also indicated no effect of TNMT on isokinetic knee extension (p = 0.57) or knee flexion (p = 0.57) strength.
Ten weeks of TNMT increased standing hip abduction strength in female athletes. Increased hip abduction strength and recruitment may improve the ability of female athletes to increase control of lower limb alignment and decrease knee loads resulting from increased trunk displacement during sports activities.
Further studies are needed to establish the degree, extent and clinical importance of these differences in the saturation of haemoglobin.
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