Short vs. Long Rest Periods Between Sets in Hypertrophic Resistance Training

Research Review: Short vs. Long Rest Periods Between the Sets in Hypertrophic Resistance Training: Influence on Muscle Strength, Size, and Hormonal Adaptations in Trained Men.

By David Boettcher MSc, BA, NASM CPT, PES, CES & NPTI

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

Original Citation: Ahtiainen, J.P., Pakarinen, A., Alen, M., Kraemer, W.J., & Hakkinen, K. (2005). Short vs. long rest periods between the sets in hypertrophic resistance training: Influence on muscle strength, size, and hormonal adaptations in trained men. Journal of Strength and Conditioning Research, 19 (3), 572-582. -- ABSTRACT

Why the Study is Relevant: Inter-set rest intervals of 30 seconds to 5 minutes have been recommended to promote hypertrophy based on a variety of rationales and physiological benefits. This 2005 study compared the effects of 2 -minute and 5 -minute rest intervals on long-term physiological adaptions, such as hormonal changes, body composition and muscle cross-sectional area (CSA). The resulting lower-intensity short rest interval and higher-intensity long rest interval programs induced similar hormonal, nervous-system, and muscular responses. This may imply that the duration of inter-set rest may not influence the magnitude of hypertrophy adaptations when intensity is sufficient.

Study Summary

Study Design	Randomized crossover design
Level of Evidence	IB Evidence from at least one randomized controlled trial
Participant Characteristics	Age:28.7 + 6.2 years Gender: Male Number of participants: 13 Inclusion Criteria: Years of experience (6.6 + 2.8) of resistance training Exclusion Criteria: Not a competitive strength athlete Not currently taking any medication that may effect physical performance.
Methodology	A familiarization session was held 1-week prior to the measurement session. Strength training sessions were completed 4 times per week throughout the 6-month study. Participants were randomly split into two groups: Lower intensity exercise with shorter rest period: (SR of 2-minutes). Higher intensity exercise with longer rest period: (LR of 5-minutes). Groups took part in one exercise regimen for 3 months before switching to the other. Different body parts were trained on different days, using multiple exercises and sets. 8-12 repetitions per set were required for all exercises. Lower body training included squats, leg presses and knee-extensions. To monitor hormone concentrations, blood samples were taken from each participant in the morning, prior to and after exercise. A minimum of 3 electromechanical dynamometer recordings were conducted to measure the voluntary isometric force of the bilateral leg-extension movement. The best performance was used for statistical analysis of isometric strength assessment. The muscle cross sectional area (CSA) of the right rectus femoris was assessed before and after the protocol. Overall body composition was estimated using skinfold thickness.
Data Collection and Analysis	A general linear model analysis of variance with repeated measures over time was performed. Body fat was measured using skinfold calipers and the Durnin and Rahaman 4 site protocol (5). Muscle cross-sectional area was assessed using magnetic resonance imaging (MRI). Dynamometer measured maximal unilateral concentric force production of the leg extensors. Isometric leg extension activity was measured using bipolar surface electrodes (by Beckman Coutler Inc.), placed longitudinally over the muscle belly and ink-marked for replicability and accuracy. EMG signal was recorded using Glonner Biomes 2000 and analyzed with the CODAS computer system. Differences between the groups were analyzed using independent samples; differences within groups were analyzed with dependent samples t-tests (p<.05).
Outcome Measures	Serum growth hormone, testosterone, and cortisol concentrations before, during and after the SR (of 2 -minutes) and LR (of 5 -minutes) acute heavy-resistance sessions Maximal isometric force production throughout the 6-month strength training period in both groups and the relative changes after SR (of 2 -minutes) and LR (of 5 -minutes) training sessions Right leg 1 RM throughout the 6-month strength training period in both groups and the relative changes after SR (of 2 -minutes) and LR (of 5 -minutes) training sessions Changes in CSA of quadriceps femoris throughout the 6-month strength training period in both groups and the relative changes after SR (of 2 -minutes) and LR (of 5 -minutes) training sessions Body composition changes throughout the 6-month training period Volume (reps x sets x weight) of exercise between the two training sessions
Results	No statistically significant changes in basal hormone concentrations were observed. A significant increase of 6.8 + 8.7% was recorded in the maximal isometric leg extension force over the 6 -month study; however, no significant difference between SR (of 2 -minutes) and LR (of 5 -minutes) was recorded. Unilateral 1RM right leg extension significantly increased over the 6 -month study; however, no significant difference between SR (of 2 -minutes) and LR (of 5 -minutes) was recorded. Muscle CSA increased by 3.5 + 4.3% over the 6 -month study, but no significant difference between SR (of 2 -minutes) and LR (of 5 -minutes) was recorded. No significant changes were recorded in the body mass or body fat percentage during the 6 -month training period. No statistically significant differences in total training load (7,065 + 2,180 kg and 7,043 + 2,208 kg) for the rectus femoris within the SR (of 2 -minutes) and LR (of 5 -minutes) groups were recorded.
Our Conclusions	The lower-intensity short rest intervals and higher-intensity long rest intervals induced similar hormonal, nervous-system, and muscular responses. When properly overloaded, the duration of inter-set rest does not influence the magnitude of hypertrophy adaptations in muscle tissue.
Researchers' Conclusions	Two different inter-set rest intervals can contribute to muscle tissue hypertrophy. Endocrine, neuromuscular and physiological adaptations occur as long as tissues are exposed sufficient mechanical stretch (overload).

Caption: Horizontal Pull-up

How This Study is Important:

This study provides evidence comparing physiological changes during a 6-month hypertrophy program using two inter-set rest intervals (2 -minutes vs 5 -minutes). When long-term changes in hormonal response, body composition and muscle cross-sectional area (CSA) were measured over-time, no significant difference was noted. This may imply that inter-set rest intervals may have less influence on hypertrophy, when intensity/load is adjusted accordingly. Further, this study may suggest that the acute hormonal and performance changes correlated with longer or shorter inter-set rest intervals, may not have an impact on long-term hypertrophy gains.

How the Findings Apply to Practice:

Hormonal and muscular responses did not differ significantly between the two inter-set rest intervals. Human movement professionals can recommend high-intensity loads with longer inter-set rest intervals (5 -minutes); or lower-intensity loads with shorter intervals (2 -minutes) to promote muscle hypertrophy. These findings match the recommendations often proposed in periodized models of training.

Strengths and Weaknesses:

This study had many methodological strengths, including:

The crossover design reduced the influence of confounding variables including individual ability, dietary measures, and sleep habits.
The weight chosen for the 10-repetition sets was based on each participant's ability level, the participants were instructed on proper technique and were familiarized with each exercise, and all exercises were performed on the same equipment for lower body training throughout the 6-month study, increasing internal validity and replicability.
The study investigated several commonly researched variables (CSA, hormone response, EMG, strength, etc.), allowing for direct comparison within the studies cohort.
This study was fairly long (6-months) relative to the body of research in strength training, allowing for significant morphological changes to be compared.

Weaknesses that should be noted:

Only 6 of the 13 participants kept consistent training logs, limiting the reliability of findings and accuracy of practical implications.
Twenty initial participants were selected, but 7 discontinued the study due to injury; limiting the power of the findings (and perhaps prompting concerns of risk of injury with the program used).
The authors noted that the participants may have been over-trained. This can negatively influence strength, stability and neuromuscular adaptations (8).
While all lower body exercises remained consistent between participants, a precise protocol was not mandated, limiting replicability.

How does it relate to Brookbush Institute Content?

The Brookbush Institute (BI) continues to refine protocols for the selection of acute variables during performance and rehabilitation programs. Consideration of all available research is essential to providing the most accurate protocols possible. Studies like the one reviewed here, provide essential data for refining acute variable protocols. This study supports the use of shorter inter-set rest intervals for lower intensity exercise, and longer inter-set rest intervals for higher intensity exercise, as is recommended by most periodized programs (including the BI). Future research should compare inter-set rest intervals less than 2 minutes in length.

Sample videos of Lower Body Strength Training below:

Deadlift with Anterior to Posterior Pull

Lateral Lunge with Front Rack Resistance:

Front Squat:

Bibliography:

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