Interference of Aerobic and Resistance Exercises (a critique and discussion), OR, The Sad State of Physical Training Academia.
In 2012 the Journal of Strength and Conditioning published a meta-study with Jacob M. Wilson as the lead author. The topic is of acute interest to this author, always looking to maintain or set new compound goals in physical training. A good run time is not enough, unless it’s a prize-winning finish (and it’s not going to be for me, not ever). One should want not just to get to a finish line in a good time, but to be able to do something substantial when one gets there.
A meta-study (a review of the data from many studies, integrating the data where compatible) is a good place to pick out some common defects in topical research literature. There are many in this topic of study, and some are serious.
The full text can be viewed at researchgate.net.
The problems with the Wilson, et al, article begin at the very top.
The title says this will be about aerobic exercise. The abstract says endurance exercise. These authors are not alone in mixing terminology. In fact their own efforts in this meta-study are hampered by different researchers using what should be precise technical jargon in different ways. How does one integrate data from different studies of the authors use different definitions between them?
The strict jargonist will insist, rightly, that aerobic exercise is that which can be sustained by that most efficient energy conversion scheme, limited only by supply of simple chemical energy to muscle cells, without diminishment of local stores. A general and literate meaning of endurance is to deliberately tolerate some level of discomfort, and this comes from exercise in many directions from different exercise intensities.
Reading the article charitably, one would assume that they mean training in the kind of exertion levels seen in long-distance competitions (e.g. running marathon). but still the term is imprecise. One could borrow from the bio-chemist and specify energy conversion modes, but we know that they do not work in isolation, and we don’t know that the chemists actually have it all figured out.
PROPOSITION – Timescale is the single best discriminator between different modes of exercise. In this context a timescale is the duration of an exercise at which something gives up and the exercise can’t be continued at the same intensity. We don’t need to know or even name the system that gives up, just that exactly one system reached its limit at that time.
The problem of imprecise and inconsistent labeling of different exertion regimes is common to the bulk of research literature on human training, not just this paper. The matter is of heightened importance in a paper which is all about different modes, which must be named. A fuller discussion will be left for another article. (It is very important, but the solution is very simple.)
The next problem is with the ancient rubric of hypertrophy – sustained swelling of muscles driven by appropriate exercise. It is one of the key variables tracked in this meta-study.
CLAIM – Hypertrophy is not a desirable sport-specific adaptation, for any activity outside of heavyweight-class bodybuilding. Of course muscle size is of keen interest to most recreational lifters, actors. models, and really most of us. But in any competitive sport, performance is what matters. The force a muscle can generate, while closely correlated to size at many timescales, is the objective variable of training. In activities where self-locomotion is important (i.e being fast), added mass is a penalty. If contact is to be made, inertia helps, but Newton will not judge if the mass involved is fat or muscle or a lunch burrito. In any weight class contest obviously mass is one’s first opponent.
Hypertrophy may be observed as a secondary marker of training success. But in most sport-focused papers it should not be a primary criteria for evaluating a training method.
The next problem in the Wilson article is another inconsistent use of imprecise terms. In the text “strength training” is used sometimes interchangeably with “resistance training”.
SIMPLE TRUTH – It’s all resistance training! Any exercise we talk about outside of space exploration bureaus is done in a gravity field. A ‘zero-load’ move like a jumping jack involves jumping a whole human body up off the ground and lifting multi-dozen-pound limbs up much farther. Running takes effort because the whole body is raised up every step, etc.
The researcher should take care to define what is meant by ‘resistance’ work, and what should be classed in with ‘endurance’ training. Is an all-out uphill sprint that exhausts the trainee in 20 seconds an endurance training regimen (actually, it is, and a very good one!) that should not be compared to a 5-rep-max all-out barbell squat effort that takes the same amount of time? (of course not!!) A useful distinction might be found, again, in timescale – how long does it take for failure to be reached, if it does? The exercise intensities in which failure is practically never reached might be the ones we call ‘endurance’ exercises.
The Wilson paper notes that the endurance/resistance distinction was pre-made arbitrarily, different data sets then sorted by percentage of max lift or percentage of VO2max, resistance and endurance data respectively.
With so many challenges to coherently merging data from studies built around different definitions, the reader should not be surprised to see poor consistency in the statistical results. Many of the stated results have confidence bands larger than the measured effect size, leaving open ready possibility of opposite results to the stated claims.
The graphical results presented show obvious quirks which beg for explanations. This endurance duration chart one would expect to be monotonic on each curve.
One could ignore troubles in that chart, were it not for the preceding figure.
The multiple reversals of the hypertrophy line scream for more detail, which is not provided. A few things that were ignored in the article are offered here as possible culprits in the poor data alignment.
– It was not noted among the groups that did strength and endurance work on the same day if it was attempted in the same session or spread out across the day. (believe it or not, some people still advocate the former!)
– In strength work the rest between sets (or between intervals of ‘endurance’ work) was not controlled for. It is known that the adaptive response in muscles varies greatly if the cells are allowed to reload and resynthesize supplies or if they are forced to repeatedly tax limited resources, the latter being hypothetically linked to greater hypertrophy and the former to greater circulatory efficiency.
– Intensity of ‘endurance’ work was not mentioned. Sustained effort in anaerobic regimes is expected to yield different results than slow disciplined workouts that try to be wholly aerobic (and a good performance program will include both).
CLAIM – Gym rats going back to the Edwardian strongmen had all this figured out (and probably some of the ancients beck to Milo of Croton). For well over a century strength and physique athletes have used body part splits together with concepts like time-to-failure to cycle through stimuli which induce continuous gains of the desired sort in different body systems.
Here in the data is a clue that coaches and researchers should take to heart and pursue. Physical training can be split in location and time and timescale to drive different responses. It is strongly suspected that a well designed study can show that what we call strength and endurance adaptations may be competing, but they are not necessarily exclusive. During training and recovery they will compete for limited resources, but if smartly and sharply split in time (day or time of day), driven by efforts at different timescales (time to failure or effort level), productive responses can be found toward any combination of training goals.
One of the few practical guides one will find to multi-mode training is The Edge from the Weider brothers.
Some research has already been done showing that not only can one get both stronger and faster, but the stronger athletes have better endurance – if the strength stimulus is intense enough to not overlap with endurance modes.
Endurance and strength training effects on physiological and muscular parameters during prolonged cycling, Christophe Hausswirth et al
Something of a bible on the topic of converting generalized training to sport-specific adaptations, collected works of Tudor Bompa will be found the shelves of many successful coaches.