Acute Effects of Complex-Contrast Exercise Performed With Two Different Intracontrast Rest Intervals on Muscle
Rohit K Thapa1, Tim S Babu1, Premraj Saini1
1Symbiosis School of Sports Sciences, Symbiosis International (Deemed University), Pune, India; and.
Journal of Strength and Conditioning Research
|July 20, 2026
Summary
Shorter intracontrast rest intervals (ICRI) in complex-contrast training do not impair muscle activation or countermovement jump performance. However, a 30-second ICRI may increase cardiovascular strain compared to a 4-minute ICRI.
Area of Science:
- Exercise Physiology
- Sports Science
- Biomechanics
Background:
- Complex-contrast training (CT) combines resistance and ballistic exercises.
- Intracontrast rest intervals (ICRI) between these exercises may influence neuromuscular responses.
- Optimizing ICRI is crucial for training efficacy and physiological load.
Purpose of the Study:
- To compare the acute effects of two different ICRIs (30 seconds vs. 4 minutes) within CT.
- To assess the impact on muscle activation, heart rate, and countermovement jump (CMJ) performance.
- To determine the optimal ICRI for neuromuscular and cardiovascular responses.
Main Methods:
- A randomized crossover study involving 11 male subjects.
- Subjects performed CT with 85% 1RM back squat and CMJ using either 30-second or 4-minute ICRI.
- Neuromuscular function, muscle activation (EMG), and CMJ kinetics/kinematics were measured pre- and post-CT.
Main Results:
- No significant differences in peak force or muscle activation during isometric knee extension, squats, or CMJs between ICRI conditions.
- Most CMJ kinetic and kinematic variables were similar across both ICRIs.
- A 4-minute ICRI maintained CMJ peak relative force at set 3 and resulted in a lower post-exercise heart rate compared to the 30-second ICRI.
Conclusions:
- Shorter ICRIs (30 seconds) do not acutely increase neuromuscular fatigue or hinder CMJ performance.
- Shorter ICRIs may lead to greater cardiovascular strain.
- Shorter ICRIs can be utilized to enhance training session density when time is limited, with awareness of the increased physiological stress.
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