Short vs. Moderate Rest Periods: Which Protocol Produces More Muscle Mass
by: Robbie Durand
Exercises that incorporate multi-joint movements can stimulate higher motor unit recruitment (e.g., fast twitch muscles) and may promote hypertrophy. Most mass programs should include the “big three” lifts (i.e., bench press, back squat, and deadlift) as a foundation. So when planning a muscle mass program, one should choose a squat over a single joint exercise such as a leg extension. Rest period length is often a topic of debate, with some trainers recommending very short rest periods for maximizing muscle mass, whereas others suggest a more prolonged rest period of 90 seconds.
When engaging in muscular hypertrophy training, the objective is to induce micro-damage to the chosen muscle groups trained to increases in protein super compensation and increase muscle growth factors (i.e. satellite cells and IGF-1) activation during rest. Another lesser known activator of muscle growth is Interleukin-6 (IL-6). IL-6 is an essential regulator of satellite cell (muscle stem cell)-mediated hypertrophic muscle growth. IL-6 is locally and transiently produced by growing myofibers and associated satellite cells, and genetic loss of IL-6 blunts muscle hypertrophy. Additional beneficial effects of IL-6 include regulation of energy metabolism, which is related to the capacity of actively contracting the muscle to synthesize and release IL-6. Paradoxically, deleterious actions for IL-6 have also been proposed, such as the promotion of atrophy and muscle wasting. IL-6 has been termed a double edge sword in the world of muscle building, much like insulin, being a power anabolic hormones yet can also lead to increases in fat mass. IL-6 is necessary for muscle growth, as it seems to kick start the muscle growth process. Muscle damage induced by the eccentric component of strength training contributes to an increase in the inflammatory process, and the infiltration of immune cells to repair and maintain tissue homeostasis.
There are a few studies that have examined the resistance exercise responses of IL-6 and rest period. One study reported no differences in IL-6 following four different bench press protocols matched for the total load with 2 min of rest between sets. This small response in IL-6 may be due to the subtle workload and more sets were needed to evoke a bigger IL-6 response. One study reported greater post-exercise IL-6 concentrations following sets of 12 repetitions at 65% 1RM compared to 3 sets of 8 reps at 85% 1 RM, with both protocols employing 2 min rest intervals. IL-6 increased immediately post-exercise compared to the control group for both exercises, with greater increases reported in the 65% 1RM group, and returned to baseline levels at 6 h with no differences found between groups IL-6.
Researchers examined the influence of the short and moderate intervals of recovery in response to an acute bout of exhaustive strength exercise on performance, inflammatory and metabolic responses in healthy adults. Eight healthy subjects performed two randomized sequences:
-Short Rest Periods= 70% of 1RM with 30 seconds of rest between sets;
-Moderate= 70% of 1RM with 90 seconds of rest between sets.
All sequences of exercises were performed over four sets until movement failure in the squat and bench press exercises, respectively. The exercise order for all sessions was squats followed by bench press. In both conditions, subjects performed 4 sets of squat and then 4 sets of bench press using 70% of the 1RM. All the sequences of exercises were performed for four sets until movement failure for each exercise with average speed (1-s eccentric and 1-s concentric actions with 1-s rest between each repetition). The total number of repetitions performed was recorded for each set of each exercise and for all sequences and used to analyze workload and performance.
At the end of the study, the results of the study demonstrate that 30 and 90-sec of recovery in between sets of upper and lower body strength exercise to failure lead to muscular fatigue, but only the 90-sec recovery period induced inflammatory and metabolic responses. Thus, different intervals of recovery in response to exhaustive strength exercise decreases performance but in only moderate intervals it is associated with an inflammatory and metabolic response. IL-6 secreted from skeletal muscle promotes skeletal muscle recovery and hypertrophy, glucose uptake. The results of this study indicate that when the load is fixed, a moderate rest interval (90 sec) results in a greater IL-6 response than a shorter rest period in recreationally resistance trained individuals, likely due to the ability to perform a higher volume of repetitions.
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