External Load, More than Surface Instability, Drives Post-Activation Performance Enhancement in Split Squat...

Area of Science:

• Sports Science
• Biomechanics
• Exercise Physiology

Background:

• Post-activation performance enhancement (PAPE) is influenced by conditioning activity (CA).
• Generalizability of back squat load-response principles to unilateral split squats with combined load and instability is unclear.
• Acute effects of stable vs. unstable split squat CA on jump performance and muscle activation require investigation.

Purpose of the Study:

• To examine the acute effects of stable vs. unstable split squat CA, with and without external load, on jump performance.
• To investigate the impact of these conditioning activities on phase-specific electromyography (EMG) of key lower limb muscles.
• To determine whether load response principles generalize to unilateral split squats under combined instability and load.

Main Methods:

• Twenty men performed a randomized crossover study with three conditioning activities (CA): unloaded stable split squat, unloaded BOSU split squat, and loaded BOSU split squat (50% 1RM).
• Jump performance (single leg jump, countermovement jump) was assessed pre- and post-CA.
• Electromyography (EMG) was recorded from eight lower limb muscles and analyzed for phase-specific activation.

Main Results:

• All CA conditions improved jump performance (SLJ and CMJ) compared to pre-test.
• Loaded BOSU split squats yielded the greatest increase in CMJ performance.
• Unloaded BOSU split squats selectively increased hamstring activation, while loaded BOSU split squats increased EMG across all measured muscles.

Conclusions:

• External load is the primary driver of acute countermovement jump potentiation.
• Surface instability alone primarily redistributes muscle recruitment towards the hamstrings without enhancing jump performance beyond stable conditions.
• For acute jump enhancement, prioritize external load; for selective posterior chain activation, consider unstable surfaces.