Thoracic-Worn Accelerometers Detect Fatigue-Related Changes in Vertical Stiffness During Sprinting

Area of Science:

• Sports Science
• Biomechanics
• Exercise Physiology

Background:

• Thoracic-worn accelerometers offer a non-invasive method for assessing running gait and neuromuscular fatigue (NMF).
• Their sensitivity in detecting speed-dependent fatigue-related gait changes remains unclear.
• Assessing NMF without additional tests like the countermovement jump (CMJ) is desirable for training and competition.

Purpose of the Study:

• To evaluate the ability of thoracic accelerometers to detect fatigue-induced changes in gait characteristics, specifically vertical stiffness (K vert).
• To assess these changes across different running speeds (3-4, 5-6, and 7-8 m·s⁻¹).
• To compare accelerometer-derived gait changes with CMJ performance following a repeated sprint protocol (RSP).

Main Methods:

• Sixteen recreationally active participants underwent pre- and post-RSP assessments.
• Assessments included single and repeated CMJs on a force plate and 40m sprints at varying speeds.
• Gait characteristics were derived from a thoracic-mounted accelerometer using a validated algorithm.
• A 12 × 40m RSP was administered between pre- and post-assessments.

Main Results:

• A significant reduction in vertical stiffness (K vert) was observed at 7-8 m·s⁻¹ post-RSP (-8.51 kN·m⁻¹).
• This decrease in K vert correlated with a significant reduction in jump height during CMJs.
• No significant changes in other gait characteristics (e.g., contact time, step frequency) were found at any speed.
• Running mechanics at lower speeds (3-4 and 5-6 m·s⁻¹) were not significantly altered post-RSP.

Conclusions:

• Thoracic-worn accelerometers can detect fatigue-related decreases in vertical stiffness during high-speed sprinting (7-8 m·s⁻¹).
• This metric may serve as a useful indicator for monitoring neuromuscular fatigue in athletes.
• A repeated sprint protocol does not appear to alter gait mechanics at lower running speeds.