Higher Baseline Aerobic Fitness Influences Jumping Performance During Military Operational Stress

Abstract

Vertical jump (VJ) testing via force plate technology serves as a field-expedient indicator of fatigue and readiness in the military. PURPOSE: To determine if higher baseline aerobic fitness is protective against declining unloaded and loaded jump performance during simulated military operational stress (SMOS). METHODS: Eighteen military men (27 ± 6 y, 84.4 ± 12.7 kg, 177.8 ± 7.6 cm) completed a 5-day SMOS protocol characterized by frequent cognitive testing, marksmanship assessments, and a ~ 90 min Tactical Mobility Test (TMT) daily. The schedule was the same each day except that subjects had four instead of eight hours of sleep and 50% instead of 100% of their caloric needs on days 2-3. Participants performed VJ testing in unloaded (UL) and loaded (LD) (16-kg) conditions at three time points during the TMT: 1) pre, 2) following 2-min water can carry, fire and movement, casualty drag, and 300-m shuttle runs (UL and LD, 16-kg) (mid), and 3) after a 4-mile ruck march (post). Subjects were divided into groups using a median split based on baseline VO2peak (HIGH vs. LOW) assessments. Three-way ANOVAs for UL and LD conditions were used to examine the effect of group*time*day on jump height (JH). RESULTS: The three-way interactions were not statistically significant. A significant group*day interaction was observed for UL condition JH (p = .035). The main effect of day from the simple two-way ANOVA was not statistically significant at each level of group (HIGH: p = .111, np2 = .218; LOW p = .312, np2 = .132), but this effect was in opposite directions. Adjusted means on days 1 to 4 declined for LOW (M: 24.7 cm, SE: 2.0 to M: 22.9 cm, SE: 1.9) but increased for HIGH (M: 27.1 cm, SE: 1.2 to M: 28.9 cm, SE: 1.3). In the LD condition, no significant interactions were observed, but there was a significant main effect of time (p = .001). For the LD condition, pre-JH (M: 21.1 cm, SE: 1.0) was significantly higher than mid-JH (M: 19.1 cm, SE: 1.1, p = .001) and post-JH (M: 19.6 cm, SE: 1.0, p = .031). CONCLUSION: We demonstrate that higher levels of aerobic fitness was protective against declining JH performance in the UL, but not LD, condition across acute SMOS, suggesting that other factors (e.g., strength/power) may be important for maintaining jump performance in the LD condition. Funded by the Department of Defense (Award # W81XWH-17-2-0070).