Phase-Specific Force And Time Metrics During Vertical Hopping In Chronic Ankle Instability

Abstract

Single limb hopping tests are used to identify motor-behavioral impairments of the lower limb associated with chronic ankle instability (CAI). Impairments are often presumed by the homogeneity of CAI cohorts with aggregate group comparisons and limited by performance-based metrics. PURPOSE: To compare phase-specific force and time metrics during single limb vertical hopping in participants with and without CAI with single-subject analyses to reveal patient-specific movement adaptations. METHODS: Individuals with CAI (n = 25; 13 M, 12F; age = 24 ± 3 y; height = 168.3 ± 12.9 cm; mass = 72.2 ± 15.2 kg) and matched controls (CON) (n = 25; 13 M, 12F; age = 24 ± 4 y; height = 172.5 ± 6.1 cm; mass = 70.8 ± 9.7 kg) completed 3 trials of 5 consecutive single limb vertical hops on a force platform on the affected and preferred limb, respectively. Eccentric and concentric phases were identified for each vertical hop from ground reaction force data and the middle 3 hops were analyzed. Peak vertical force (PVF), time to peak vertical force (TTP), vertical impulse (VI), and phase time (PT) were obtained for each phase. Groups were compared with an unpaired t-test. The Model Statistic procedure was used to test for CAI individual differences with an aggregate CON mean. RESULTS: Concentric PT (p = .041; CAI: 0.23 ± 0.09 s; CON: 0.19 ± 0.0 s; d = 0.53) and TTP (p = .020; CAI: 0.08 ± 0.19 s; CON: 0.03 ± 0.02; d = 0.71) were longer in CAI. While not significant (p = .066), a moderate effect (d = 0.45) was observed for concentric VI between CAI (3.04 ± 0.56 Ns/kg) and CON (3.40 ± 0.91 Ns/kg). Ten CAI participants exhibited less concentric PVF (CAIrange: 15.16-21.07 N/kg; Mdiff = 4.38 ± 1.99 N/kg; d = 0.80-3.39). Eight CAI participants displayed longer concentric TTP (CAIrange: 0.06 - 0.43 s; Mdiff = 0.11 ± 0.05 s; d = 1.58 - 8.03) and longer PT (CAIrange: 0.22 - 0.56 s; Mdiff = 0.15 ± 0.12 s; d = 0.82 - 4.21) compared to CON. Additionally, 10 CAI participants displayed less eccentric TTP (CAIrange: 0.07 - 0.11 s; Mdiff = 0.04 ± 0.02 s; d = 1.00 - 2.91) than CON. CONCLUSION: Individuals with CAI displayed differences during the propulsion phase of repetitive hopping on the affected limb and suggests difficulty transitioning from eccentric to concentric phases. This could reveal a less efficient transfer of lower limb mechanical output from the affected limb during repetitive vertical hopping.