From twitch to relaxation: Obesity dysregulates muscle contractile function

Area of Science:

• Neuromuscular Physiology
• Obesity Research
• Translational Science

Background:

• Obesity is increasingly recognized as a condition affecting neuromuscular function.
• Impaired muscle strength relative to body mass is a known consequence of obesity.
• The impact of obesity on muscle contraction dynamics requires further investigation.

Purpose of the Study:

• To investigate the effects of obesity on muscle force generation.
• To determine if obesity alters muscle contraction and relaxation dynamics.
• To assess the translational impact of obesity on neuromuscular function from mice to humans.

Main Methods:

• Assessed contractile properties of extensor digitorum longus (EDL) and soleus (SOL) muscles in control (CN) and diet-induced obese (OB) male mice in vitro.
• Evaluated plantar flexor performance in normal-weight (CN) and class I obese (OB) sedentary men using maximal voluntary isometric contractions and a dynamic calf raise test.
• Compared specific force, rates of force development, and relaxation kinetics between obese and control groups in both species.

Main Results:

• Obese mice exhibited lower specific force and slower rates of force development and relaxation in both EDL and SOL muscles compared to controls.
• Obese men demonstrated a lower rate of torque development and prolonged relaxation kinetics of plantar flexors.
• Obese men had a higher body mass to maximal voluntary isometric torque ratio, contributing to slower calf raise phases.

Conclusions:

• Obesity negatively impacts muscle force generating capacity.
• Obesity induces slower muscle contractile kinetics, affecting both force production and relaxation.
• These findings highlight significant neuromuscular impairments associated with obesity across species.