#39 – How We Get Stronger, Faster, and More Enduring: The SRA Cycle

Last episode we posed the question: why do our workouts have to be so hard? The scientific answer to this question lies in the concept of the stress-recovery-adaptation cycle, or SRA cycle, derived from Hans Selye’s work in the first half of the twentieth century. Simply put, in order to generate an adaptation, which we would recognize as an increase in one or more of the ten general physical skills (strength, endurance, mobility, etc), then you must progressively increase the amount of stress applied during the training program. That is the nature of training: it must become “harder” over time to continue driving progress.

In the 1950’s Austro-Hungarian endocrinologist Hans Selye developed a theory known as the general adaptation syndrome which describes the effect of acute stress, generated by a stimulus (real or imagined), on an individual. Selye observed that the effect of stress on an organism was to disrupt homeostasis and, if continued unchecked, eventually kill the organism. If the stress was removed and the organism was given sufficient time and resources to recover from the stress, then it adapted to the stress in a manner specific to the type of stress imposed.

From this work, strength and conditioning coaches have gleaned the concept of the stress-recovery-adaptation (SRA) cycle, which guides the programming decisions behind our training model. Put simply, an athlete wishing to get stronger, faster, or more cardiovascularly fit must be subjected to a workout which stresses her, then recover from that workout by eating and sleeping. When this process is repeated over a period of time, she begins to see results and — voila! — she has performed what we call training, or a systematic, planned series of workouts toward a goal.

This is a key observation that we first covered in episodes #1-10 but we must restate now: in order to get stronger (or faster, or more fit, etc.), you must perform exercises which stress your muscles enough to disrupt homeostasis. This is why our workouts inevitably become hard — they must generate enough stress to drive an adaptation. And this should be obvious; if you keep lifting the same weight every workout, you cannot get stronger. You are already adapted to that weight, thus there is not sufficient stress to disrupt homeostasis. One of the programming variables has to change — you must do more reps, use more weight, or otherwise increase the volume or intensity of the exercise to drive adaptation. Yet, we see this time after time in the gym. People perform the same exercises, with the same number of sets and reps, with the same weight, over and over again, expecting results but not getting them. In short, these people are merely exercising when they should be training.

At first, just about anything constitutes a stress. For the completely sedentary person, a walk around the block is probably stressful enough to make them both stronger and more fit. This is known as the novice effect, and explains why people get results in the short-term for nearly anything. As Mark Rippetoe, the author of Starting Strength: Basic Barbell Training, is fond of saying, for rank novices “riding a bike will make their bench press go up.” Beyond this point, however, a good training program that incrementally increases stress to drive adaptation over a long period of time is needed. Fortunately, novices can make progress nearly every workout for the first few months of their training. In this case the SRA cycle is very short, about 48-72 hours long.

Eventually the novice can no longer add stress to the workout and make progress. This is easiest to observe in barbell training. The novice adds five pounds to the bar each workout, but cannot complete the prescribed number of sets and reps. At this point, he must start adding weight every other workout, and perhaps perform a lighter workout in between, in order to add weight to the bar. Eventually adding weight every other workout becomes every week, then every two weeks, then monthly, and for the advanced athlete nearing their genetic potential for strength, every few months. In these cases, the SRA cycle is stretched over a period of time rather than a single workout.

Though it’s beyond the scope of this episode, recovery is equally important. It is, after all, half of the equation. When we recover from a stressful workout our brain makes new neural connections and becomes more efficient at recruiting motor units for the task, our muscles grow, our cells become more efficient at generating ATP and eliminating waste products. Food and sleep are the primary components of recovery. The important thing to keep in mind here is that as you add stress to a training program, the recovery must keep pace, or you risk overtraining and stalling progress, losing progress, and even injury.


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