Original paperJump-landing direction influences dynamic postural stability scores
Introduction
Approximately 50,000 anterior cruciate ligament (ACL) reconstructions are performed each year in the United States causing a financial impact of $850 million per annum.1 Furthermore, the occurrence of ankle sprains has been estimated to be 5000 every day in the United Kingdom2 and between 23,000 and 27,000 every day in the United States.2, 3 Based on two investigations, the annual aggregate dollar expenditure for moderate to severe ankle sprains in the United States was estimated to be approximately $3.65 billion in 2003. As a result, the need to conduct more functional and dynamic testing has emerged. Therefore, the examination of lower extremity dynamic joint stability has become a focus of many clinicians and biomechanists around the world.
The ankle and knee joints rely heavily on the dynamic restraints (muscular stiffness) of the lower extremity in an attempt to prevent injury, which has been suggested to provide greater joint stability.4, 5 More specific, it is thought that preparatory muscle activity is primarily responsible for joint protection.6, 7 One technique to indirectly measure muscular stiffness is dynamic postural stability. McKinely and Pedotti indicated that subjects with greater and earlier preparatory muscle activity demonstrated improved dynamic postural stability scores.6 Currently, two measures of dynamic postural stability are mentioned in the literature: (1) time to stabilization and (2) the dynamic postural stability index (DPSI). Both measures determine how well balance can be maintained while transitioning from a dynamic to static state and are also functional measurements of neuromuscular control because they are calculated during a single-leg-hop-stabilization protocol. However, the DPSI was found to be a more reliable (ICC = 0.96) and precise (standard error of the measure = 0.03) measure of dynamic postural stability than time to stabilization.8
The majority of previous investigations have focused on pathologies; specifically anterior cruciate ligament (ACL) deficiency or ankle instability. Time to stabilization evaluated differences among healthy, ACL deficient, and ACL reconstructed patients,9 and between healthy and ankle instability patients.10, 11, 12 Similarly, the DPSI examined differences between healthy and ankle instability patients.24 However, all of the aforementioned investigations used a forward jump-landing protocol despite a lack of empirical evidence supporting its use. Examining the differences in dynamic postural stability among different jump-landing directions could reveal previously overlooked information regarding neuromuscular control and may allow clinicians and researchers to develop better injury prevention strategies in a clinical population. Therefore, the purpose of this investigation was to evaluate how dynamic postural stability is affected when performing a jump-landing task in three different directions (forward, diagonal, lateral) using the DPSI.
Section snippets
Subjects and design
A one-within repeated measures design was used to determine if jump-landing direction (forward, diagonal, lateral) would affect dynamic postural stability. Twenty-six recreationally active subjects [10 males (22 ± 3.9 years of age, 70.9 ± 7.6 kg, and 176.8 ± 6.5 cm) and 16 females (20.6 ± 0.5 years of age, 65.6 ± 9.1 kg, and 166.4 ± 5.9 cm)] volunteered to participate in this investigation. Recreationally active was operationally defined as exercising at least three times a week for a minimum of 30 min each.
Results
The group means, standard deviations and effect sizes for the directional DPSI can be seen in Table 2. The MLSI revealed a significant difference among directions [F(2, 50) = 41.41, p < .001]. Tukey's-post-hoc (HSD = 0.021) test showed that all three directions were significantly different from each other with α = 0.05. More specifically, the lateral jump-landing protocol produced significantly higher scores than the diagonal and forward jump-landing protocol. In addition, the diagonal jump-landing
Discussion
It is thought that lower extremity joints are stressed regardless of direction during a jump protocol. This is due to the functional anatomy of the lower extremity joints which allow tri-planar motion.17, 18 Therefore, pathological groups which have shown dynamic postural stability deficits (i.e. ACL deficient, or chronic ankle instability) could be tested using any jump-landing direction and still have their postural control deficits exposed. For example, previous work by Ross et al. has
Conclusions
The results of this investigation indicate that in a healthy population, the direction of the jump protocol will affect dynamic postural stability in the frontal and vertical planes. More specifically, lateral and diagonal jump-landings produce increased MLSI scores and forward jump-landings produce increased VSI scores. As a result of the current findings, we can conclude that conducting all research with a forward jump-landing protocol is not entirely valid to evaluate causes and prevention
Practical implications
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Using forward jump-landing protocols alone, may mask potentially harmful deficits when conducting an investigation or making a return to play decision.
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Researchers and clinicians need to vary the selection of the jump-landing protocol according to the athlete or group of athletes that they are testing.
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