[Application df/dt(max) index for determinations of skeletal contractility]

Area of Science:

• Exercise physiology
• Skeletal muscle biology
• Biomechanical analysis

Context:

• Skeletal muscle contractility is crucial for physical performance and is influenced by training.
• Assessing muscle function requires sensitive and reliable indicators.
• Previous studies have primarily focused on maximum force (Fmax) as a key metric.

Purpose:

• To evaluate the maximum rate of force increase (+dF/dt(max)) and the maximum rate of force decrease (-dF/dt(max)) as more sensitive indices of skeletal muscle contractility.
• To compare the efficacy of these indices against maximum force (Fmax) under varying training loads.
• To investigate the relationship between skeletal muscle supermicro-structure and contractile function.

Summary:

• Mice undergoing swimming training showed significant increases in Fmax, -dF/dt(max), and notably +dF/dt(max) with regular myoneme structure and increased mitochondria.
• Overtraining led to reduced Fmax, -dF/dt(max), and a more pronounced decrease in +dF/dt(max), accompanied by mitochondrial depletion and myoneme disorganization.
• +dF/dt(max) demonstrated greater sensitivity to changes in skeletal muscle function compared to Fmax and -dF/dt(max) across different training states.

Impact:

• Establishes +dF/dt(max) as a superior biomarker for assessing skeletal muscle contractility changes due to exercise and overtraining.
• Provides insights into the ultrastructural adaptations of skeletal muscle in response to training.
• Informs the development of more precise training protocols and injury prevention strategies in sports science and rehabilitation.