Trunk Muscle Activation in the Back and Hack Squat at the Same Relative Loads

Area of Science:

• Biomechanics and Exercise Physiology
• Strength and Conditioning Research

Background:

• The hack squat (HS) typically allows for a greater one-repetition maximum (1RM) than the back squat (BS) due to trunk support.
• This trunk support in the HS may reduce trunk muscle activation (TMA), potentially leading to different training adaptations compared to the BS.

Purpose of the Study:

• To compare 1RM and TMA between BS and HS at relative loads of 65%, 75%, 85%, and 95% of maximal system mass.
• To determine the influence of load on TMA during both squat variations.

Main Methods:

• Ten male participants completed three test sessions: 1RM testing for BS and HS, neuromuscular test familiarization, and neuromuscular testing.
• Neuromuscular testing involved performing three repetitions at four relative submaximal loads (65-95% of 1RM) for both BS and HS.

Main Results:

• Mean HS 1RM and submaximal loads were significantly higher than BS.
• Trunk muscle activation was significantly greater in the BS compared to the HS across most muscles and phases, except for the rectus abdominis during the concentric phase.
• TMA increased with increasing load for both exercises and phases, with the exception of the lumbar sacral erector spinae in the HS eccentric phase.

Conclusions:

• Despite higher absolute loads in the hack squat, the back squat elicits greater trunk muscle activation.
• Trunk muscle activation is load-dependent in both BS and HS.
• The back squat is arguably more effective than the hack squat for developing trunk strength and stability, crucial for dynamic athletic performance.