|Rest is not a waste of time ;-)|
Eventually, it can thus not be surprising that James McKendry and colleagues write in their latest paper that "short rest (1 min) between sets of moderate-intensity, high volume resistance exercise blunts the acute muscle anabolic response compared with a longer rest period (5 min), despite a superior circulating hormonal milieu," and conclude that their "data have important implications for the development of training regimens to maximize muscle hypertrophy" (McKendry).
What may be surprising, though, is the extent (see Figure 2) to which the post-exercise protein synthesis the researchers measured in young male subjects who habitually performed lower-limb resistance training at least once per week for ≥1 year prior to study enrollment and were deemed ‘recreationally trained’, when they had them do the same leg workout
- 4 sets of leg press and 4 sets of knee extension exercise at 75% of 1RM
- performed w/ a lifting-lowering cadence of ~1 sec in both concentric & eccentric phases,
- without pause, until momentary muscular failure (i.e. 9-10 on the Borg CR-10 scale).
|Figure 1: Overview of the initial (Trial 1) and next morning procedures (Trial 2 | McKendry. 2016).|
|Figure 2: Protein synthetic (myofibrillar) and hormone response after working out with 1 vs. 5 min rest (McKendry. 2016).|
|Figure 3: Sign. associations between PWO hormone levels and lean mass, as well as fiber size increases (West. 2012).|
Why do other studies not confirm this finding? I guess that depends on the study. An often-cited paper by Kraemer, et al. for example found 1 minute of rest to outperform 3 minutes hypertrophy-wise - probably because the 1-min rest protocol involved 3 sets of 8 exercises with a 10-RM load, while the 3 minute protocol involved "only" five sets of five exercises, performed with a 5-RM load, so that the two workouts were not volume equated and the study no comparison of workouts with different rest times, but rather one of hypertrophy vs. strength workouts.The existing differences in anabolic signaling protein phosphorylation (e.g. p70S6KThr389, rpS6Ser240/244, 4EBP1Thr37/46, etc.) can likewise not serve as a mechanistic explanation. After all, these are the switches that trigger the growth. Saying they are responsible would be tantamount to saying that the light switch is the reason the light went out, when someone actually switched it off.
Conflicting results from other studies, e.g. Villanueva, et al. (2015) who found sign. greater muscle gains in with 1 vs. 4 minutes of rest, may be explained by differences in the study population (elderly in Villanueva, et al.) and/or the training protocol, which did not involve training to failure and thus probably didn't produce significant volume advantages for the 4-minute rest group. Eventually, volume appears to be, within sustainable limits, the most sign. determinant of the hypertrophy response to exercise, so if you do something to increase it (e.g. myoreps or real vs. volume- equated drop sets, etc.) you may still benefit. If you simply cut the rest, however, the volume suffers from not resting long enough (cf. table on the left) and this may affect your gains.
|Acute effect of different rest intervals between sets over the number of repetitions maximum (RM). Values expressed as RM (de Salles. 2009)|
So, what is it that makes the difference? Well, in view of the results of previous studies that suggest that, ultimately, it's not hormones, not protein phosphorylation, but rather the total volume of weight that is lifted (at least unless that's so much that you do more harm than good) that determines the hypertrophy response to resistance training (Schoenfeld. 2013), we should look at a different study outcome: the total volume in kilograms (see Figure 4):
|Figure 4: Set- and total volume when subjects trained with 1 vs. 5 minutes rest (McKendry. 2016).|
- Bottaro, Martim, et al. "Effects of rest duration between sets of resistance training on acute hormonal responses in trained women." Journal of science and medicine in sport 12.1 (2009): 73-78.
- de Salles, Belmiro Freitas, et al. "Rest interval between sets in strength training." Sports Medicine 39.9 (2009): 765-777.
- Goto, Kazushige, et al. "Muscular adaptations to combinations of high-and low-intensity resistance exercises." The Journal of Strength & Conditioning Research 18.4 (2004): 730-737.
- Henselmans, Menno, and Brad J. Schoenfeld. "The effect of inter-set rest intervals on resistance exercise-induced muscle hypertrophy." Sports Medicine 44.12 (2014): 1635-1643.
- Kraemer, WJ, Marchitelli, L, Gordon, SE, Harman, E, Dziados, JE, Mello, R, Frykman, P, McCurry, D, and Fleck, SJ. Hormonal and growth factor responses to high intensity resistance exercise protocols. J Appl Physiol 69: 1442-1450, 1990.
- Schoenfeld, Brad J. "Postexercise hypertrophic adaptations: a reexamination of the hormone hypothesis and its applicability to resistance training program design." The Journal of Strength & Conditioning Research 27.6 (2013): 1720-1730.
- Schoenfeld, Brad J., et al. "Longer inter-set rest periods enhance muscle strength and hypertrophy in resistance-trained men." Journal of strength and conditioning research/National Strength & Conditioning Association (2015).
- Villanueva, Matthew G., Christianne Joy Lane, and E. Todd Schroeder. "Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men." European journal of applied physiology 115.2 (2015): 295-308.
- West, Daniel WD, and Stuart M. Phillips. "Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training." European journal of applied physiology 112.7 (2012): 2693-2702.
- Willardson, Jeffrey M. "A Brief Review: How Much Rest between Sets?." Strength & Conditioning Journal 30.3 (2008): 44-50.