Measuring what matters in isometric multi-joint rate of force development

Area of Science:

• Sports Science
• Exercise Physiology
• Biomechanics

Background:

• Neuromuscular fatigue assessment is crucial for understanding training adaptations and performance.
• Isometric force-time measures, including peak force and rate of force development (RFD), are commonly used to evaluate neuromuscular function.
• Different testing protocols may influence the sensitivity of these measures to fatigue.

Purpose of the Study:

• To compare the responsiveness of two isometric squat test (ISqT) protocols to neuromuscular fatigue.
• To determine if isometric peak force (ISqT^peak) and isometric explosive force (ISqT^exp) protocols can be used interchangeably for assessing fatigue-related changes in force and RFD.

Main Methods:

• Ten resistance-trained participants underwent high-intensity strength training (8 sets of 3 back squats).
• Isometric peak force (ISqT^peak) and isometric explosive force (ISqT^exp) protocols were administered at knee angles of 100° and 125° pre-training, immediately post-training, and 24-h and 48-h post-training.
• Standardised response means (SRMs) were calculated to assess the responsiveness of peak force and RFD measures.

Main Results:

• Peak force measured by the ISqT^peak protocol at 100° knee angle showed the highest responsiveness (SRM = -1.97).
• The ISqT^exp protocol at 125° knee angle was most responsive for RFD measures (SRM = -1.31 for RFD 200 ms).
• Peak force was the most responsive variable with the ISqT^peak protocol, while RFD was more responsive with the ISqT^exp protocol.

Conclusions:

• The ISqT^peak protocol is more sensitive to changes in peak force, while the ISqT^exp protocol is more sensitive to changes in RFD following high-intensity resistance training.
• These findings suggest that the ISqT^peak and ISqT^exp protocols should not be used interchangeably for evaluating RFD variables due to differing sensitivities to neuromuscular fatigue.