(14) NEUROMUSCULAR IMPAIRMENTS IN COUNTERMOVEMENT JUMP PERFORMANCE FOLLOWING HEAT AND EXERCISE STRESS EXPOSURE

Purpose: To examine the effects of a 2-phase heat and exercise stress (HES) protocol on countermovement jump (CMJ) performance. Methods: Fourteen participants (age: 32.1±12.6yrs) completed the procedures. To induce fatigue, participants underwent a 2-phase HES protocol, beginning with 1hr of passive heat exposure in an environmentally controlled room set at 27°C, followed by 90min of stationary cycling under the same thermal conditions. During the HES participants were not allowed to drink water or eat. Following the immediate post-HES exposure testing participants were provided 500mL water and allowed to passively recover for 45min. At each time point (pre-HES, post-HES, and 45min recovery), participants performed 2 CMJ on force plates (30s of rest between jumps). A repeated-measures ANOVA examined CMJ metric changes, with generalized eta squared (η²G) effect sizes used to assess magnitude of differences. Bonferroni paired t-tests were conducted for post-hoc pairwise comparisons when significant main effects were observed. To further analyze CMJ performance, Principal Component Analysis (PCA) was used to reduce dimensionality, and the transformed data trained a Random Forest (RF) model to predict Pre-HES Post-HES, and Recovery states. Feature importance analysis identified the top 5 principal components (PCs), and the highest-contributing CMJ variables were extracted to determine metrics differentiating fatigue states. Results: Following the HES protocol, CMJ performance exhibited significant decrements (Table 1), with jump height (p=0.005, η²G=0.191) and peak power (p=0.003, η²G=0.072), decreasing from pre-HES to post-HES and remaining suppressed during recovery. During the CMJ eccentric (ECC) phase, deceleration rate of force development (RFD) significantly (p=0.001, η²G=0.224) declined post-HES, while ECC peak force was reduced (p=0.023, η²G=0.054). ECC duration was (p=0.036, η²G=0.067) longer in the recovery phase compared to pre-HES. For the concentric (CON) phase, both CON impulse and mean power decreased post-HES (p< 0.001, η²G=0.064-0.097), with impairments persisting into recovery. In the landing phase, peak landing force was lower post-fatigue (p=0.041, η²G=0.080), while force asymmetry decreased (p=0.023, η²G=0.151). The RF model successfully classified HES and recovery states (100% accuracy). PC1, which captured peak power, takeoff velocity, and jump height, was the most important predictor of HES state. PC3 and PC2 (ECC metrics), primarily associated with deceleration RFD and ECC peak force, also played a significant role in classification. Conclusions: The findings indicate substantial neuromuscular impairments in CMJ performance post-HES, particularly in force-generating capacities during the ECC and CON phases, with persistent reductions in some measures despite a recovery period. Practical Applications: The PCA+RF approach may aid in fatigue classification, offering potential applications in sport and tactical athlete populations for workload management and injury prevention strategies. Acknowledgements: None