Learn more about this integral, yet often overlooked element of your training programme
By Pedro Van Gaalen, Editor
During training our muscles derive the energy they need to contract from different energy systems, depending on the load, intensity and duration of the specific exercise. All of these factors combine to ‘overload’ and impose a certain degree of stress on the muscle or group of muscles being used. In addition the nervous system fatigues to some degree, depending on the overload, and the energy system being targeted becomes depleted. The by-products of exercise, such as lactic acid and pyruvate, which can limit exercise capacity, also begin to build up.
Due to these factors we need to rest our muscles during exercise, be it active rest or a complete cessation of activity, to give them time to recover, replenish energy stores, remove lactic acid and return to a state where they are able to efficiently contract once again. The duration of these rest periods is dependent on a number of factors, yet many gym-goers and active individuals give very little thought to the amount of time they rest between sets. These rest periods also play an important part in eliciting your desired outcome, be it increased muscle size, enhanced strength or fat loss.
The Eenergy Systems
The amount of rest needed between sets is generally governed by the dominant energy system used while exercising, which is determined by the type of exercise you are doing and the type of muscle (slow or fast twitch) you are targeting. The three main energy systems used to drive muscle contractions are:
- ATP-PCr (Adenosine Triphosphate Phosphocreatine) system – Responsible for very short duration, power-based exercise that lasts for up to 10 seconds. The energy-producing reactions occur in the absence of oxygen (anaerobic) and don’t produce lactic acid.
- Anaerobic (a.k.a. gylcolytic) system – Supplies energy for exercises that generally last less than two minutes. This would be the primary energy system used for general weight lifting.
- Aerobic (a.k.a oxidative) system – Supports long duration, lower intensity activity by supplying oxygen to working muscles. This supplies energy for step classes, spinning and running. For example, during a 1km run this system is already providing approximately half of all the energy requirements, while during a marathon it provides 98% or more.
In terms of how energy production and replenishment governs the duration of your rest periods between sets, the ATP-PCr system takes at least three minutes to recover fully (convert adenosine diphosphate or ADP back into usable ATP) after a high-intensity set, which shouldn’t last more than 10-15 seconds of all-out effort. The general guideline for rest periods between powerlifting, one rep max or plyometric exercise sets is 5 minutes, to allow for complete recovery.
Your anaerobic or glycolytic energy system can keep your muscles contracting at a high intensity for about a minute or two before it begins to run out of fuel. Glycolysis relies on energy from ATP, which has been converted from carbohydrates (glucose), to fuel the high-to-medium intensity sets commonly used by bodybuilders, athletes looking to improve performance, or those looking to burn fat or lose weight. During this type of contraction the build-up of lactic acid and hydrogen ions, a by-product of glycolysis, will eventually start to inhibit muscle contraction. When this happens you need to rest for a short period (less than two minutes) to allow for at least partial recovery and the removal of these by-products. Another reason for keeping rest periods short enough for only partial recovery is the fact that the more you overload your glycolytic system, the better you’re able to buffer these ions and the faster you can recover between sets of medium-to-high-intensity exercise. Shorter rest periods are also better for hypertrophy (building more muscle) as it imposes more stress on the muscle. This is what promotes muscle cell regeneration during the post-exercise recovery period.
Owing to the nature of weight training, in any form, the aerobic or oxidative energy system is not generally engaged. However, recent research suggests that the oxidative system is heavily involved in the recovery process between sets of high-intensity anaerobic work like squats. If you intend doing high intensity cardio work such as interval sprints or fartlek training that lasts less than five minutes, then the ideal rest period is 1-5 minutes. If your intervals are 20 minutes or more then you should rest for 5-10 minutes between efforts to allow for at least partial recovery.