Abstract
This study explored the notion that identification of a “directional bias”, believed to identify dynamic postural stability deficits, provides a tool to rehabilitate patients with individual-specific biased (asymmetric) exercises that are matched to these deficits (matched bias exercises).
Aims:
1. To determine the inter-tester reliability of the directional bias assessment.
2. To investigate the validity of the directional bias assessment, by determining immediate effects of directionally biased exercises on dynamic postural stability and muscle performance (H1) and comparing these outcomes to baseline measures (H2).
Participants:
Thirty-three participants aged 18-50 years with a history of more than one unilateral musculoskeletal lower limb injury.
Methods:
1. Inter-tester reliability of the directional bias assessment: Two researchers independently assessed each participant’s directional bias and categorised these into four sub-groups, using left or right bias (the poorer performing side) plus an extension or flexion bias (the pelvic position in which participants had better dynamic postural control, and resulting performance during single heel raises and hopping). Results were compared using the Kappa coefficient and the prevalence-adjusted and bias-adjusted kappa (PABAK) coefficient.
2. Validity of the directional bias assessment: A randomized repeated measures cross-over design was used. Participants performed directionally biased intervention exercises in the matched bias (MB) and unmatched bias (UB) directions, with the order randomly allocated. Two outcome measures, Time to stabilisation (TTS) during a single-leg landing, and rebound hopping, were assessed before and following each exercise intervention. Ground reaction force data were used to calculate TTS in the anterior posterior (AP) and medial lateral (ML) directions, as well as the median time in the air (flight) and on the ground (land) during rebound hopping. T-tests were used to investigate differences in outcome between the MB and UB exercises, in accordance with the Altman methods for analysing cross-over trials (H1) and Repeated Measure ANOVAs were used to investigate differences between Baseline, MB and UB measures for both outcomes (H2).
Results:
1. Inter-tester reliability: Agreement was achieved for 27 of 33 directional bias assessments (82%), with a kappa of K = 0.75 and a PABAK adjusted kappa of K = 0.76.
2. Validity of the directional bias assessment:
H1: Following MB exercises ML TTS was significantly faster compared with UB exercises (3.05 ± 0.91s vs. 3.52 ± 1.17s, P = 0.02), however, AP TTS (P = 0.15) was not significantly different. Land was significantly shorter following MB exercises compared with UB exercises (MB 0.40 ± 0.09 s vs. UB 0.41 ± 0.10 s, P = 0.05), however, flight (P = 0.24) was not significantly different. Although not statistically significant, period effects and treatment-period interactions were demonstrated, and thus their presence cannot be ruled out, and may have resulted in lowered treatment effects and the non significant results.
H2: Within-participants effects (Baseline, MB and UB) demonstrated significantly decreased AP TTS, (P = 0.049), land (P = 0.041) and increased flight (P =0.016). Compared to Baseline a significant decrease in AP TTS (P = 0.008) was found following MB exercises, and significantly shorter flight followed UB exercises (P = 0.036). No other comparisons were significant.
Conclusions:
1. Inter-tester reliability: “Substantial” inter-tester reliability was found for the directional bias assessment for individuals with previous lower limb injury.
2. Validity of the directional bias assessment: An immediate 15.4% improvement in dynamic postural stability, as well as significantly less variance between tests, was found following MB vs. UB exercises. Together with an immediate and significant improvement following MB vs. UB exercises for rebound hop, provides support for H1: that MB is superior to UB exercise. In comparison to baseline measures, statistically significant improvements were found in AP TTS and land following MB exercises, with UB exercises detrimental to flight during rebound hopping, both of which support (H2): that from baseline an immediate measurable improvement will result following MB exercises and an immediate degradation following UB exercises.
The immediate improvements demonstrated in this present study may indicate neurophysiologic mechanisms at the central nervous system level, that may lead on to improvements in the residual deficits and decreased re-injury rates known to occur following lower limb injuries. However, further research is needed to evaluate this.