Research-based Exercise Prescription Part 2
Every month, new studies that support the health benefits of exercise are published in scientific journals. The take-home message is that exercise is good for you in many ways including some that we would have never imagined even just a few years back. However, it’s important to stress that the term “exercise” has many connotations such that some people dedicate a lot of time to activities that they consider exercise, but science-supported research does not. This is why an educated consumer is the best customer in the gym.
Those who understand that training recommendations should be developed according to research-based constructs speak of the science of exercise prescription. In other words, much like a doctor prescribes a drug that has stood the scrutiny of scientific investigation, legitimate exercise professionals apply similar standards when establishing exercise guidelines. However, it’s apparent that this is often not the case in the field where hearsay and unsupported claims run rampant. And nowhere is this more apparent than in the weight room. Consequently, it behooves anyone who dedicates at least some of their gym time to resistance training (and everybody should!) to look to the research when deciding how to do so. A good place to start is a recent article by Ogasawara et al. in the Journal of Applied Physiology.Entitled, “mTOR signaling response to resistance exercise is altered by chronic resistance training and detraining in skeletal muscle,” this study examined some very important changes that occur in the body after only one resistance training session. The authors begin by explaining that skeletal muscle possesses dynamic tendencies that allow it to adapt to changes in activity. For example, after you perform a resistance exercise session, synthesis of muscle proteins is accelerated and these proteins will continue to accumulate when the stimulus is repeated during subsequent sessions. This is why your muscles grow bigger (hypertrophy) as weeks pass when you lift weights regularly. However, there is also a tendency for skeletal muscle to strive to maintain constancy (homeostasis). Consequently, once an adaptation occurs, there is a reduced response in the future. This is why people like myself who have been training with weights for decades have not accumulated 500 pounds of muscle by now!
Collectively, the ability to hypertrophy when challenged coupled with the drive for homeostasis means that you can convince your body that it needs more muscle up to a point beyond which it says, “No mas!” And this makes sense because just like not enough muscle can threaten survival, too much also has potential drawbacks. So, with this in mind, it’s easy to understand why resistance training-induced protein synthesis and subsequent hypertrophy occur most rapidly during the early phases of training before progressively slowing with time. But it’s also interesting to note that after a period of detraining, muscle adaptive responses return to their initial levels such that the effects of training once it is resumed are similar to those that were observed when the training stimulus was initially encountered. The aim of this study was to assess why these changes occur by monitoring activation of important signaling proteins that mediate the process. These include those associated with both mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK).
To begin this study, the authors assigned 20 male rats to one of four groups. Rats in group one performed one exercise bout only, while those in groups two and three performed one bout per day on non-consecutive days for a total of 12 and 18 bouts, respectively. Like the first group, rats in the fourth group also performed one exercise bout, but did so after completing the 12-bout protocol followed by 12 days of detraining. The activation that constituted training for these rats involved electrical stimulation of the right gastrocnemius muscle of the calf. The current, which was applied via needle electrode, forced the muscle to contract isometrically (i.e., develop tension without changing length) at its maximal capacity five times per set with five sets performed per session. Conversely, the left gastrocnemius was not trained and, therefore, served as a control against which adaptations of the right side were compared. Twenty-four hours after their final training session, the rats were anesthetized and their muscle tissues were removed for analysis.
Results from this study showed that an increase in muscle weight indicative of hypertrophy was present after 12 and 18 training sessions, but not after one. Furthermore, when 12 days of detraining followed 12 training sessions, the increase after cessation of training remained. Not surprisingly, peak tetanic torque (a measure that within this model is synonymous with strength) reacted similarly as it was increased after multiple training bouts and this measure was also unaffected by detraining. However, analysis of some of the signaling responses painted quite a different picture. For example, mTOR downstream targets p70S6K and rpS6 were elevated above the control value after only one exercise bout. However, repeated bouts actually blunted this effect such that an elevation was still present, but of lesser magnitude. Even more interesting was the finding that the maximal response, which was observed for group one, was also observed in the fourth group when 12 trainings sessions were followed by 12 days of detraining and one bout that resumed it.
This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.
