Has anyone experienced improved strength and muscle gains by increasing their rest intervals between sets? The past couple of years I?ve followed very short rest intervals, i.e., between 45-90 seconds depending on the number of reps.
I think you explained the reason for your recent success in your second sentence. If you’ve been using the same rest periods for several years, you were due for a change and it’s no surprise that your body responded as it did.
WARNING! Very simplified explanation of muscular hypertrophy to follow. In other words don’t jump down my throat for omitting some things.
The dominant energy system used for short duration, high intensity exercise is the ATP-PC system. Once the cellular reserves of ATP-PC are depleted, your body will rely more on fast glycolysis for energy production. Fast glycolysis is the breakdown of stored carbohydrates without oxygen.
Once you’ve depleted ATP-PC stores by doing a set of heavy squats, or a 100 meter sprint, it ~ 3 minutes for those stores to be restored. If you attempt another set of squats, or a sprint before the 3 minute mark, you force your body to rely more on fast glycolysis for energy. Since FG is not capable of supplying ATP as rapidly as the ATP-PC cycle, your strength/speed will go down on subsequent sets.
So what does this mean? Muscular hypertrophy that results from short rest period training is not only the result of accruing more contractile protein, but also from more stored carbohydrate and the water, enzymes etc. needed to use it. Muscular hypertrophy that results through training with complete rest periods is more likely to be solely from more contractile protein.
So the best type of training really depends on your goals. If getting bigger is one of your main goals, don’t abandon short rest periods. Take a look at Chad Waterbury’s TBT workout. That program is a great example of how to periodize not only sets, reps, and exercises, but also rest periods since it switches from straight sets to supersets from week to week.