Dynamic Postural Stability During Rested and Fatigued Backwards Single-Leg Jump-Landings

Abstract

Poor time to stabilization (TTS) during backward single-leg jump-landing (BSLJL) is a risk factor for injury. PURPOSE: The purpose of this study was to assess the reliability of TTS and effect of fatigue on TTS. It was hypothesized that TTS would demonstrate adequate reliability, and that fatigue would worsen TTS. METHODS: Nine active subjects (4 F, 5 M, 24.8 ± 3.4 y, 1.77 ± 0.08 m, 74.7 ± 15.3 kg) performed BSLJL on the dominant (D) and non-dominant (ND) leg. BSLJL was performed barefoot by jumping backwards on the test leg over a 0.15 m hurdle, landing on the test leg on a force plate with hands on the hips, and stabilizing as quickly as possible. During session 1, subjects performed 10 trials without familiarization. During session 2, subjects performed 3 trials (PRE), rested for 5 minutes, and re-performed 3 trials (POST). During session 3, subjects completed a 5 to 7 minute fatigue protocol consisting of step-ups, L-drills, vertical jumps, and agility ladder drills between PRE and POST instead of resting. Sessions 2 and 3 were completed in a randomized order. TTS was quantified as time from initial contact to when vertical ground reaction force remained within 5% of the subject’s body mass for 1 s. RMANOVA and paired t-tests were used to compare TTS, and typical error (TE) was used to quantify reliability. Significance was set to p ≤ 0.05. RESULTS: During session 1, BSLJL TTS did not improve over 10 trials on D (p = 0.18) or ND (p = 0.49). During session 2, TTS was similar PRE and POST on D (1.12 ± 0.47 vs 1.17 ± 0.40 s, p = 0.81) and ND (1.27 ± 0.53 vs 1.05 ± 0.57 s, p = 0.09), and had a within-day TE of 0.02 and 0.16 s, respectively. During session 3, TTS was similar PRE and POST on D (1.21 ± 0.32 vs 1.60 ± 1.05 s, p = 0.22), but greater at POST compared to PRE on ND (1.21 ± 0.51 vs 1.60 ± 0.58 s, p = 0.04). The between-day TE assessed using PRE TTS from session 2 and 3 was 0.36 s on D and ND. CONCLUSION: BSLJL learning effects are negligible, although familiarization trials are likely needed. Between-day reliability does not appear adequate. Using TTS to longitudinally monitor injury risk may be inappropriate. Fatigue appears to degrade TTS, but does not affect all subjects equally, and effects may be masked by large inter-subject variation in TTS. Identifying factors related to susceptibility to fatigue induced decrements may improve injury prevention measures.