Previously in our blog series, we learned the significance of rest between workout days to avoid burnout. However looking on a micro-scale, it is important to understand optimization of rest periods during resistance training when trying to lose weight. Before understanding optimal recovery between sets, we must define the culprit of initial onset muscle fatigue during resistance training; lactic acid.
Lactic acid is the waste product of a carbohydrate which fuels anaerobic glycolysis, the preferred energy pathway during resistance exercise (McArdle, Katch & Katch, 2010). The accumulation of lactic acid in the muscle is suggested to inhibit cross bridge cycle (AKA muscle contraction) therefore, emerging as one of the factors of early onset fatigue when performing mechanical work.
Now to examine the clearance or removal of this lactic acid. It is important to understand not ALL of this lactic acid can be removed or cleared acutely. A portion of this lactate will remain present in the fibers, the hydrogen ions will dissociate and cause soreness in the coming days (Brooks at al., 2002). However, a large portion of it can be removed via active recovery.
Active recovery, in terms of its meaning during resistance training, refers to any aerobic activity performed intermittently with resistance exercise to assist with removal of lactic acid. This removal is carried out primarily via the Cori Cycle, a process which shuttles this lactic acid to the liver to be reverted back to a carbohydrate, which can be used for fuel (McArdle Katch & Katch, 2010). The removal of this lactic acid will do two things; improve your ability to complete work (sets & reps) throughout your resistance workout, thus allowing more calorie expenditure, secondly it will prevent accumulation of lactic acid and prevent delayed onset muscle soreness (DOMS). Therefore, it is clear the benefit is two fold. You are able to burn more calories during a given resistance bout, and you will WANT to keep working out since not a lot of people enjoy being debilitatingly sore after resistance exercise.
In conclusion, the next time you are feeling fatigued during resistance exercise, don't head to the water fountain or sit on your phone for five minutes. Hop on any piece of aerobic equipment and exercise at a low intensity for those five minutes. Your body will thank you and most importantly you will maximize calorie expenditure.
Brooks, G. A. (2002). Lactate shuttle–between but not within cells?. The Journal of physiology, 541(2), 333-333.
McArdle, William D., Frank I. Katch, and Victor L. Katch. Exercise physiology: nutrition, energy, and human performance. Lippincott Williams & Wilkins, 2010.