Affiliations: Department of Physical Therapy, Georgia State University, Atlanta, GA, USA
Correspondence:
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Corresponding author: Liang-Ching Tsai, Department of Physical Therapy, Georgia State University, P.O. Box 4019, Atlanta, GA 30303, USA. Tel.: +1 404 413 1246; E-mail: ltsai@gsu.edu.
Abstract: BACKGROUND: While extreme changes in body position (e.g., standing vs. sitting) have been shown to affect knee extensor strength, little is known regarding how less extreme changes in body position affect knee extensor strength and activation. OBJECTIVE: This study evaluated the effect of four seated positions on the maximum voluntary isometric contraction (MVIC) and electrically-evoked isometric strengths of the knee extensors. METHODS: Forty healthy subjects participated. MVIC strength, electrically-evoked strength, and voluntary activation of the quadriceps muscles were measured under four seated positions: 1) 22.5–25∘ forward tilt, 2) 0∘ tilt, 3) 22.5–25∘ backward tilt, and 4) 45–50∘ backward tilt. The effect of seated position on each dependent variable was assessed using a one-way repeated measures ANOVA with linear contrasts. RESULTS: MVIC and electrically-evoked strengths increased (P⩽ 0.037) by 5–11% as the body was moved from the 22.5–25∘ forward-tilted to 45–50∘ backward-tilted position. However, voluntary muscle activation and EMG amplitudes of the knee extensors during MVIC did not change. CONCLUSIONS: Knee extensor MVIC and electrically-evoked strengths were modestly enhanced as the body was tilted backwards. The use of a semi-reclined position may assist in obtaining a more forceful contraction of the knee extensors, thereby potentially resulting in better strength training outcomes.
