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I would like to thank Dr Baxter for her kind words regarding the
importance of my manuscript in highlighting the ambiguity in the use of
the term intensity in the exercise sciences. I also agree fully that more
careful definition might help to clarify the issue of its use. However, I
think that better clarification of the definition of the term only further
serves to highlight the issues associated with its use.
In correspondence with another academic in this area it was pointed
out that my manuscript did not in fact discuss Intensity as defined under
the Systeme International d'Unites which is power transferred per unit
area (i.e. W.m-2). Further that in luminescence the term is defined
differently again (candela per square metre i.e. cd.m-2). A number of
manuscripts in previous years have discussed the misuse of Newtonian
mechanical constructs in describing exercise and yet have opted for the
continued use of intensity to describe the difficulty or 'hardness' of
exercise (Knuttgen, 1978; Winter & Fowler 2009). I maintain that
attempting to describe exercise in such a way is perhaps a wasted effort.
If, for example, we use 'Intensity' as defined under the Systeme
International d'Unites as power transferred per unit area, and it is
expressed as the unit watts per square metre (i.e. W*m-2), then
technically any use of the term outside of this strict definition would
constitute a misapplication, assuming it is taken to be the accepted
definition in that context. This would also apply to the suggestions made
by other authors (Knuttgen, 1978; Winter & Fowler 2009) more recently
to use the term to describe how 'hard' exercise is but to differ the unit
dependent on the context. Unless power per unit area is being measured or
discussed would it perhaps not be better to avoid the term altogether in
exercise science? If so then the word 'Intensity' could be avoided
completely by just using the phrase 'power per unit area'. Alternatively,
the problem appears to me that many within exercise science are probably
more likely to consider the OED definition of 'Intensity' and as noted in
my article the term becomes redundant once the construct being measured
(and preferably the unit of measurement) is made clear. Further, the
suggestion to avoid the word 'Intensity' entirely (unless referring to
power per unit area) in order to avoid confusion is exemplified by the
confusion that could occur from the situation (albeit unlikely) that the
magnitude of 'power per unit area' is being considered. Both the SI and
OED definition could be applied and result in curious statements such as
"Intensity (OED Definition) OF Intensity (SI Definition)" (i.e. "Intensity
OF W*m-2") which is very confusing (albeit rather amusing). Indeed,
another proverbial can of worms could be opened by noting that 'hardness'
is already considered a measurable variable in itself which refers to
either scratch, indentation or mechanical resistance of minerals. Perhaps
we should also leave this term alone as well except in colloquial verbiage
and 'difficulty' or 'challenge' might be better suited. These could be
defined along the lines of 'the overall demands of exercise relative to a
person's immediate ability to meet those demands'. Neither term to my
knowledge is currently under use with different application in other
scientific disciplines such to cause confusion.
I agree fully with Dr Baxter's comments that variables such as 'load'
and 'perception of effort' can indeed vary dependent upon the context.
However, this does not seem to me to be a terminological issue as it is
known that almost all dependent variables that can be measured may in fact
differ dependent upon manipulation of other independent and confounding
variables. For example, load measured by a 1RM may vary dependent upon
number of factors such as those noted by Dr Baxter and thus the 1RM should
be considered within the context of those factors. If one particular
context permits a higher 1RM than all others it may be fair to say that
this is indeed the individual's true maximum to the best of our knowledge.
In this case using Dr Baxter's example that in such instances where 1RM
may be reduced "...the (reported) intensity of the session would be higher
despite lower loading...", instead it could be said that the loading
relative to the true maximum was lower, however, relative loading under
the circumstances was still maximal (a 1RM under the current conditions)
despite a lower absolute loading. Similarly, perception of effort may
differ dependent upon a number of factors despite the same exercise
conditions being performed and indeed that many person's ability to rate
their perception of effort on a continuum is poor. Indeed a good example
of this, and which suggests even advanced trainees are not so good at
predicting how close they are to their maximum effort, is seen where such
trainees are asked to predict the number of repetitions they could perform
to momentary muscular failure and initially under predict (Hackett et al.,
2012). Perception of effort is also often confused with perceptions of
discomfort or other physical sensations, as noted in my manuscript, which
further confound this and suggests that the two should be differentiated
in measurement and in reference.
In any case, it would appear that Dr Baxter along with most others
persistence that 'intensity' should be used, albeit in combination with
the unit of measurement being considered or "...defined in terms of
reliable measures with which to underpin the definition in the respective
study..." appears a redundant suggestion and a potentially confusing one.
If the term intensity to describe the 'hardness' (difficulty/challenge?)
of an exercise can be defined differently in different contexts dependent
upon the variable being examined it potentially opens up many to again
misinterpret its meaning. Why not instead just refer to the variable being
considered (e.g. load, effort, heart rate, force/torque etc.) whilst
considering the context under which it is being measured/examined?
1. Kunttgen HG. Force, work, power and exercise. Med Sci Sport
2. Winter EM, Fowler N. Exercise defined and quantified according to
the Systeme International d'Unites. J Sports Sci 2009; 27(5):447-460
3. Hackett DA, Johnson NA, Halaki M, Chow CM. A novel scale to assess
resistance-exercise effort. J Sports Sci 2012;30:1405-1413
Clarification on the definition of use of the term 'intensity' as
raised by Steele certainly serves to highlight the continuing variation -
and confusion - around use of this term. Due to the ambiguity as to
whether intensity is a measured load or is synonymous with perceived level
of exertion, Steele recommended abandonment of intensity as a descriptive
However it is my belief that the very dichotomy rai...
However it is my belief that the very dichotomy raised by Steele
emphasises the need to quantify and define the term through the
development and adoption of reliable and objective outcome measures, and
ones that capture the dichotomy: i.e. the psychological (perceived level
of exertion) and physiological (load) components of intensity.
Translation and definition of terms are fundamentally important in
the communication of science: in fact the imperative of research papers
reporting the details of the research methods employed depends in turn on
the definition and language used to communicate the methods.
While I acknowledge that there are inherent problems in translation
of the term intensity, I further believe there are issues surrounding the
choice of definition being either 'load', or 'perception of exertion'.
For example, an individual's maximum 'load', or 1RM, is not constant:
rather, it represents a hypothetical 'best'. It fails to recognise
differing circumstances, including human factors, and instead assumes a
mechanistic uniformity in ability for 1 RM. However, there are a number of
factors which may affect the ability of a individual to achieve a 1RM,
including stressors; injury or muscle tightness; pre-fatigue from other
lifts; DOMS (delayed onset muscle soreness); or even calorific deficit or
inadequate nutrition. In such instances the measured load of 1RM would be
altered (albeit transiently), but the (reported) intensity of the session
would be higher despite lower loading.
'Load' also does not capture other factors which affect the 'load'
such as 'time'; if the lift is slowed down then there is more effort
exerted without altering the load. Other ways of increasing the intensity
of a lift without altering the load include reduced rest periods, more
repetitions and 'concentration' sets whereby the person is restricted to
main area of the workload (such as in squats the bottom half of range of
Similarly there are challenges in advocating intensity as being
synonymous with perceived level of exertion, which requires the objective
ability of the participant to distinguish with accuracy the effort
required in a given exercise session. This presents two problems: often
the complete novice participant has low experience in determining what
their effort is on a continuum, when compared to (say) that of the
experienced lifter/athlete. Further to this, there is the issue that, both
the novice and advanced lifter are inclined to responder bias in such
circumstances. Although for the advanced lifter their experience while
provide a more accurate quantification of perceived level of exertion
(perhaps due to more instances for comparison), in both cases the accuracy
is contingent on the responder (and their associated prior
It is my recommendation that intensity is not a term that becomes
neglected or ceases to be used. The term must instead be defined in terms
of reliable measures with which to underpin the definition in the
respective study. These outcome measures should reflect the dual nature,
and therefore, ambiguity in translation: they should include both
physiological and psychological concepts, and measures. This would include
and capture the level of exertion used while providing a more scientific
foundation for replication.
Jump to comment:
I would like to thank Dr Baxter for her kind words regarding the importance of my manuscript in highlighting the ambiguity in the use of the term intensity in the exercise sciences. I also agree fully that more careful definition might help to clarify the issue of its use. However, I think that better clarification of the definition of the term only further serves to highlight the issues associated with its use.
Clarification on the definition of use of the term 'intensity' as raised by Steele certainly serves to highlight the continuing variation - and confusion - around use of this term. Due to the ambiguity as to whether intensity is a measured load or is synonymous with perceived level of exertion, Steele recommended abandonment of intensity as a descriptive word.
However it is my belief that the very dichotomy rai...