Resistance Training Part 9
Last installment, I detailed a number of scientific investigations that reported gains in both strength and muscle mass from resistance training even though it was done with a much lighter weight than that which would typically be deemed appropriate. The key distinction was that in these studies, blood flow to the working musculature was blocked as the sets were being performed. The take-home message was that high mechanical stress, per se, was not necessary to make muscles grow bigger and stronger. But it¹s also interesting to note that when high mechanical stress is present (i.e., when you are working against relatively challenging loads during a resistance training set), blood flow is similarly impeded, even though no extraneous device (e.g., a blood pressure cuff) is involved. The reason is because when you¹re lifting a relatively heavy weight, intramuscular pressure is high and blood vessels in the region are momentarily crimped during the sticking point of each repetition. In conjunction with these new findings, this suggests that it is blood flow restriction simultaneous with contractile activity that makes our muscles respond. The next thing to consider is why.
Shinohara et al. were the first to show that light-load training was effective for making muscles stronger if blood flow was blocked while the sets were being performed. The researchers explained that impaired blood flow while muscles were contracting resulted in elevated energy transfer with reduced oxygen availability. A natural consequence was the accumulation of metabolites that would interfere with muscle contractility. Typically, when light loads like these were encountered with unrestricted flow, no similar effect would take place. The end result was an increase in fatigue and corresponding requirement for increased nervous system activity (e.g., activation of muscle fibers that typically would not be required to move similar loads).
Muscles get stronger from resistance training for two general reasons enhanced nervous system function (e.g., an increased number of fibers recruited and recruitment with greater activation frequency and possibly synchronicity) and an increase in contractile protein that causes growth. In 2000, Takarada et al. provided evidence that the strength gains that occurred consequent to light-load training with restricted flow was a function of the latter effect. This allowed for a more extensive description of the series of events that had been suggested previously. They suggested that metabolite accumulation and, specifically, intramuscular acidification that occurred due to anaerobic metabolism under oxygen-deficient circumstances would lead to activation of a chemoreceptive reflex that caused greater stimulation of the sympathetic branch of the autonomic nervous system. Proof of this was the greater level of circulating norepinephrine (a sympathetic neurotransmitter) that they found after light-load training with restricted flow. Sympathetic activation is synonymous with fiber activation, so this was consistent with the increased muscle electrical activity (measured via electromyography) that they also found. The end result was that growth hormone was released in high quantities after exercise in order to adapt to the stress that had been encountered. Growth hormone brings muscle growth that makes a muscle less susceptible to similar stress in the future.
There are a number of practical implications of these findings. Obviously, it isn¹t feasible to restrict blood flow when lifting weights in a non-laboratory setting and, even if it was, there aren't many muscle groups where such an intervention could be realistically employed. But it¹s important to recognize that a similar series of adaptive events can take place if we perform conventional resistance exercise (i.e., lifting weights without an extraneous device that limits blood flow) so long as we do so properly. An important observation from the Shinohara study was that their subjects reported light-load training felt quite different when the tourniquet was applied. Specifically, the isometric repetitions they were performing were very difficult and, in fact, near maximal during the final 30 seconds of the three-minute set, even though the amount of force they were applying against the immovable arm was still relatively low. In essence, fatigue had reduced their muscles¹ capacity to contract such that less force (or, by extension, less weight if an actual weight had been being moved) was sufficient to get the job done.
The bottom line is that a heavy weight is not required during resistance training, but a heavy effort is. You have to induce fatigue in a relatively short period of time and the best way to do this is by using a challenging weight (e.g., one that you cannot move continuously for greater than 60-90 seconds). But it¹s important to realize that if continuous repetitions with a given amount of weight becomes a near-maximal effort in 60 seconds, it will be no more beneficial to use a heavier weight and encounter the same degree of difficulty in 30 seconds because you¹ll only reach the same ultimate end point and it is that end point (as opposed to what brought you there) that dictates the response. The same is the case for speeding up your reps or loosening up your form so that you can lift more weight for the same time interval. However, a weight that you can move for a much longer period of time can never do the trick, no matter how many repetitions you perform.
This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.
