Longer Interset Rest Periods Enhance Muscle Strength and Hypertrophy in Resistance-trained Men

Research Review: Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men

By Nicholas Rolnick SPT, MS, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Schoenfeld, B.J., Pope, Z.K., Benik, F.M., Hester, G.M., Sellers, J., Nooner, J.L., Schnaiter, J.A., Bond-Williams, K.E., Carter, A.S., Ross, C.L. and Just, B.L. Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. J Str Cond Res. July 2016; 30(7): 1805-1812. ABSTRACT

Why the Study Is Relevant: Load, volume and duration of interset rest periods are commonly adjusted variables in programs designed to build muscular strength and hypertrophy. Load and volume modulation have been extensively researched and are acknowledged as primary factors in promoting positive muscular adaptations (1). However, research on whether longer or shorter interset rest intervals promote greater adaptations in muscle strength and hypertrophy (2-3) has offered conflicting conclusions. This 2016 study from Lehman College in New York suggests that within the study's population of young resistance-trained males, longer rather than shorter interset rest periods produce greater muscular hypertrophy and strength.

Caption: Model: Nicholas Rolnick

Model: Nicholas Rolnick

Study Summary

Caption: The back squat was one of the lifts used during the study. Both groups improved their 1RM post-intervention, but the longer interset rest group improved significantly more than the short interset rest period group.

The back squat was one of the lifts used in the study. All participants improved their 1RM post-intervention, but the longer interset rest group improved significantly more than the short interset rest period group.

Review & Commentary:

The study investigated the effect of longer and shorter interset rest intervals on muscular strength, hypertrophy and endurance in resistance-trained males over an eight-week period. The results align with current recommendations for training for maximal strength, but conflict with current guidelines for maximizing hypertrophy. More research is needed to clarify the effect of interset rest intervals on muscular endurance.

The study had several strengths, including:

• The study had a strong, well documented methodology. Resistance training studies are often difficult to perform due to the time commitment needed from the subjects and the researchers, difficulty in creating a standardized protocol, and the difficulty controlling for covariates (such as nutritional intake) in the analysis. The protocol discouraged nutritional supplementation (with the exception of a post-workout shake) and any additional lifting to the study protocol in an attempt to further isolate the variable of interest (the interset rest period).
• The study used a validated protocol for 1RM, 10RM and endurance muscle testing; citing all necessary references.
• The use of ultrasound technology helped strengthen results. Ultrasound technology is a reliable and validated way to measure to detect small changes in muscle thickness (4). By recording each subject's muscle thickness before and after the study, the authors could relate changes in muscle thickness to their primary outcome measures. Previous studies have used anthropometric measurements to determine changes in muscle size. (5). However, anthropometry lacks specificity for detecting small changes in muscle mass unless paired with ultrasound (6).
• Selecting seven exercises commonly used by human movement professionals and the training public to promote muscle strength and hypertrophy, increases the relevance and practicality of the study.

Weaknesses that should be noted prior to integration of the findings include:

• Resistance training programs most often last longer than eight weeks. While significant differences were noted, it is not clear whether these differences were the result of altering a variable, or rest time unto itself. Further, if training continued for 16, 24 or even 52 weeks, would the neuromuscular system adapt to a shorter rest period, eventually providing the same benefit as longer rest periods.
• Although it may still be common to use horizontal load schemes in certain settings (set, rest, set, rest, set rest, next muscle), with the popularity of circuit and metabolic training, further research is needed to determine how longer rest times for each muscle group may be affected by active rest or working other muscle groups during the rest period.
• Further research should be done, limiting total session time; a practical issue. Although this study did not aim to examine "best use" of session time, it may be interesting to compare longer and shorter rest periods in conjunction with matched lifting session length. In essence, this would result in a study comparing the results gained by longer rest periods, against the loss in total volume limited by session length.
• Although each subject was told not to alter nutritional intake after beginning the program, nutritional intake was not controlled. Future research should include a food journal to minimize the chance that diet influenced outcomes.
• Muscle thickness measurements were taken at only one place. Previous research has shown regional muscular hypertrophy can occur (7). It is unknown if the Short group exhibited greater hypertrophy in regions that were not measured. Future research should use multiple measurements sites for each muscle to provide greater clarity.

Why This Study is Important

The study provides evidence that longer rest periods (3 minutes) favor muscle strength and hypertrophy compared to shorter rest periods (1 minute). Specifically, longer rest periods result in significantly greater anterior thigh thickness and a trend towards upper arm hypertrophy. The results conflict with current recommendations for muscle hypertrophy, which suggest shorter rest intervals (<90 seconds) to promote metabolic accumulation and adaptation (8), especially for larger movement patterns and muscle groups.

Increased muscular endurance was also strongly correlated (r = 0.75) with 1-repetition bench press in both groups, implying that longer rest periods may be more beneficial for endurance as well. It has been presumed that shorter rest periods forced an adaptation that increased the muscle's ability to buffer metabolites (9). Conversely, increasing maximal strength could be an alternative strategy to improving endurance by reducing the relative metabolic cost per repetition. More research is needed in different populations and with different weightlifting experiences to make conclusions on this topic.

How the Findings Apply to Practice

When designing an exercise regimen for clients or patients, it is important to understand how interset rest duration influences muscular adaptations. This study suggests that longer rest periods are likely ideal for hypertrophy and maximal strength training. However, altering the interset rest duration is one strategy to achieve greater strength, muscle hypertrophy and muscular endurance. Other variables include frequency, volume, load and repetitions.

While longer interset rest intervals were shown to promote larger gains in hypertrophy and strength, it is important to consider that the longer rest interval group took nearly twice as long to complete each session. Total session time is an important consideration when creating an exercise program for any individual. Further, one six-month case-crossover study showed that muscular adaptations were similar in a 2-minute and a 5-minute interset interval in recreationally-trained men using similar movements (10). This may imply that 2-minute rest periods may be sufficiently long (instead of 3 minutes), or that within 6 months of training the body may adapt to shorter rest periods.

Based on the results of this study, larger differences were noted between the shorter and longer rest interval groups in larger muscles and during compound movement patterns. Human movement professionals may be able to achieve most of the benefits of longer rest periods while maintaining more reasonable session lengths, by using longer rest periods between compound multi-joint exercises (squats , bench press , deadlifts ) and shorter rest periods between single-joint exercises (bicep curls, leg extensions, etc.).

Additional research is needed to determine whether this is an optimal strategy to maximize muscular gains and change body composition.

Related Brookbush Institute Content

The Brookbush Institute (BI) recommends varying interset rest periods based on the individual's training goals. The findings of this study support the BI's recommendation of a 2 to 3 minute rest period for programs targeting maximal muscular strength and power. Unfortunately this study does not address circuit training, which BI commonly uses during resistance and performance training to reduce overall session time, and/or allow for more attributes of physical performance to be addressed during a given session length.

BI stresses the importance of goal oriented training and individualization of routine/program design in the consideration of all acute variables, including interset rest period. If goals include maximizing muscular strength and hypertrophy, and session time is not a limiting factor, rest periods should be increased based on this high quality study. At the very least, longer rest periods between compound multi-joint exercises (squats , bench press , deadlifts ) and shorter rest periods between single-joint exercises (bicep curls, leg extensions, etc.) should be used.

The following videos depict BI recommendations to reinforce optimal motor patterns for similar exercises to those used in this study:

Brookbush Institute Videos

Back Squat

Bench Press and Chest Press

Kneeling Cable Pulldown (Lat Pulldown Progression)

Front Squat to Shoulder Press

References:

1. Krieger JW. Single vs. multiple sets of resistance exercise for muscle hypertrophy: a meta-analysis. J Str Cond Res. April 2010; 24(4): 1150-1159.
2. Villanueva MG, Lane CJ, Schroeder ET. Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men. Eur J Appl Physiol. Feb 2015; 115(2): 295-308.
3. Henselmans M, Schoenfeld BJ. The effect of inter-set rest intervals on resistance exercise-induced muscle hypertrophy. Sports Med. Dec 2014; 44(12): 1635-1643.
4. Mickle KJ, Nester CJ, Crofts G, Steele JR. Reliability of ultrasound to measure morphology of the toe flexor muscles. J Foot Ankle Res. April 2013; 6(1): 12
5. Buresh R, Berg K, French J. The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training. J Strength Cond Res. 2009; 23: 62-71.
6. Bemben MG, Sato Y, Abe T. The use of anthropometry for assessing muscle size. Int J Kaatsu Training Res. 2005; 1: 33-36.
7. Mendiguchia J, Garrues, MA, Cronin JB, Contreras B et al. (2013). Nonuniform changes in MRI measurements of the thigh muscles after two hamstring strengthening exercises. J Strength Cond Res. 2013; 27(3): 574-581.
8. National Strength and Conditioning Association's Foundation to Fitness Programming. Accessed: 12/28/2016. https://www.nsca.com/uploadedFiles/NSCA/Resources/PDF/Education/Tools_and_Resources/FoundationsofFitnessProgramming_201508.pdf
9. Kraemer WJ, Noble BJ, Clark MJ, Culver BW. Physiologic responses to heavy-resistance exercise with very short rest periods. Int J Sports Med. 1987; 8(4): 247-252.
10. Ahtiainen JP, Pakarinen A, Alen M, Kraemer WJ. et al. Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men. J Strength Cond Res. August 2005; 19(3): 572-582.

© 2017 Brent Brookbush

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