Dynamic stability is often measured by time to stabilization (TTS), which is calculated from the dwindling fluctuations of ground reaction force (GRF) components over time. Common protocols of dynamic stability research have involved forward or vertical jumps, neglecting different jump-landing directions. Therefore, the purpose of the present investigation was to examine the influence of different jump-landing directions on TTS. Twenty healthy participants (9 male, 11 female; age = 28 ± 4 y; body mass = 73.3 ± 21.5 kg; body height = 173.4 ± 10.5 cm) completed the Multi-Directional Dynamic Stability Protocol hopping tasks from four different directions—forward, lateral, medial, and backward—landing single-legged onto the force plate. TTS was calculated for each component of the GRF (ap = anterior-posterior; ml = medial-lateral; v = vertical) and was based on a sequential averaging technique. All TTS measures showed a statistically significant main effect for jump-landing direction. TTSml showed significantly longer times for landings from the medial and lateral directions (medial: 4.10 ± 0.21 s, lateral: 4.24 ± 0.15 s, forward: 1.48 ± 0.59 s, backward: 1.42 ± 0.37 s), whereas TTSap showed significantly longer times for landings from the forward and backward directions (forward: 4.53 ± 0.17 s, backward: 4.34 0.35 s, medial: 1.18 ± 0.49 s, lateral: 1.11 ± 0.43 s). TTSv showed a significantly shorter time for the forward direction compared with all other landing directions (forward: 2.62 ± 0.31 s, backward: 2.82 ± 0.29 s, medial: 2.91 ± 0.31 s, lateral: 2.86 ± 0.32 s). Based on these results, multiple jump-landing directions should be considered when assessing dynamic stability.
Kathy Liu and Gary D. Heise
Gabrielle Stubblefield, Jeffrey Tilly and Kathy Liu
Joint integrity is compromised after an ankle sprain. However, little is known when comparing acute and subacute alterations after an ankle sprain to a preinjury baseline. The purpose of this study was to examine acute and subacute changes in joint laxity after a lateral ankle sprain. Eighty-nine NCAA Division I collegiate athletes that participated in basketball, soccer, and volleyball were recruited. Ankle joint laxity was measured with an instrumented ankle arthrometer during preseason for baseline measurements. Throughout the year, six individuals were diagnosed with a mild lateral ankle sprain. The injured ankles were re-measured at 24 hr, 3 days, 3 weeks, 5 weeks, and 6 months postinjury and compared to baseline measurements for changes in joint laxity. The greatest increases in laxity were seen 3 days, 3 weeks, and 5 weeks postinjury. The findings from this study support the current recommendations for diagnosing ankle sprains. Clinicians should access preinjury baseline measurements for comparison after injury to aid in rehabilitation progression throughout the recovery process after an injury.