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Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat

Paulo Henrique Marchetti1, Josinaldo Jarbas da Silva2, Brad Jon Schoenfeld3

  • 1Graduate Program in Science of Human Movement, College of Health Science (FACIS), Methodist University of Piracicaba, 13423-070 Piracicaba, SP, Brazil; Institute of Orthopedics and Traumatology, School of Medicine, University of São Paulo, Laboratory of Kinesiology, 05403-000 São Paulo, SP, Brazil.

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Summary

The maximal isometric back squat exercise activates lower limb muscles differently based on knee joint angle. Muscle activation, particularly in the quadriceps and gluteus maximus, varies significantly with position, with 90° showing the highest overall activation.

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Area of Science:

  • Biomechanics
  • Exercise Physiology
  • Sports Science

Background:

  • The back squat is a fundamental resistance exercise.
  • Understanding muscle activation patterns is crucial for optimizing training.
  • Knee joint angles significantly influence biomechanics during squats.

Purpose of the Study:

  • To compare lower limb muscle activation during maximal isometric back squats.
  • To investigate the effect of three knee joint angles (20°, 90°, 140°) on muscle activation.
  • To identify muscle-specific responses to varying isometric squat positions.

Main Methods:

  • Fifteen healthy, resistance-trained men participated.
  • Maximal isometric back squats were performed at 20°, 90°, and 140° knee angles.
  • Surface electromyography (sEMG) measured vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM) activation.

Main Results:

  • Quadriceps (VL, VM, RF) activation was generally highest at 90°.
  • Gluteus maximus (GM) activation was significantly greater at 20° and 90° compared to 140°.
  • Biceps femoris (BF) and semitendinosus (ST) showed similar activation across all tested knee angles.

Conclusions:

  • Knee joint position significantly alters muscle activation patterns in the quadriceps and gluteus maximus during isometric back squats.
  • An isometric back squat at 90° elicits the highest overall muscle activation.
  • An isometric back squat at 140° results in the lowest activation for the vastus lateralis and gluteus maximus.