A Muscle Physiology-Based Framework for Quantifying Training Load in Resistance Exercises.

Area of Science:

• Exercise Physiology
• Sports Science
• Biomechanical Analysis

Background:

• Current objective training load (TL) indexes in resistance training (RE) lack physiological significance.
• There is a need for a more physiologically relevant method to quantify TL in RE.
• Understanding muscle physiology is key to improving TL assessment.

Purpose of the Study:

• To develop a muscle physiology-based approach for quantifying TL in resistance exercises (REs).
• To investigate physiological responses to different resistance training intensities.
• To explore the impact of fatigue kinetics on TL quantification.

Main Methods:

• Fifteen participants underwent individual torque-velocity profiling.
• Participants performed isokinetic leg extension sessions at low, moderate, and high intensities (LI, MI, HI), with volume-equated loads using the 'volume-load' (VL) method.
• Systemic and local physiological responses, including mechanical work, torque, impulse, rate of force development (RFD), and electromyographic activity, were measured.

Main Results:

• Significant differences in mechanical work, normalized torque, mechanical impulse, and RFD were observed across intensities.
• RFD was primarily affected by repetition accumulation, with impairments noted at low-intensity/long-series and high-intensity protocols.
• Muscle function impairments correlated with RFD rate decay and electromyographic changes, suggesting fatigue kinetics are crucial.

Conclusions:

• A generic equation for muscle fatigue rise could enhance TL quantification in RE.
• Integrating muscle fatigue kinetics and utilizing dimension reduction methods improve the physiological description of RE responses.
• A multidimensional approach considering various TL indexes is essential for practical field applications.