Functional Demand Increases With Task Difficulty Following Acl Reconstruction

An assessment of quadriceps muscle capacity during gait and landing has yet to be explored in an ACL reconstructed population throughout rehabilitation, though is warranted due to the known muscle deficits following surgery. Functional demand is the ratio between joint moment and muscle strength and has been explained as muscle capacity used during a task. PURPOSE: The purpose of this study was to examine the changes in functional demand between the ACL and NonACL limbs following ACL reconstruction during gait and a single limb hop. METHODS: Twenty-five individuals (13F; Age 23.3 ± 8.6 yrs; Height 1.7 ± 0.07 m; Mass 75.3 ± 11.7 kgs) completed two testing sessions following ACL reconstruction, the first 4.4 ± 0.4 months, and the second 9.0 ± 0.4 months after surgery. Individuals completed bilateral isometric quadriceps strength testing, and biomechanical testing utilizing 3D motion capture and force plates to assess overground gait biomechanics and a single limb hop for distance. Knee moments were calculated using inverse dynamics. Functional demand was calculated as the peak knee moment divided by peak strength for each limb. A 2x2 repeated measures ANOVA (limb x time) was used to compare functional demand between limbs over time during gait. A 2x2 repeated measures ANOVA (limb x task) was used to compare functional demand between gait and single limb hop. Bonferroni multiple comparison procedures were used post hoc. RESULTS: The limb x time interaction and both main effects were not significant for functional demand during walking (p > 0.05). There was, however, a significant interaction between limb and task for functional demand (p < 0.001). Functional demand in the ACL limb (111.5 ± 27.3%) was lower than in the NonACL limb (134.3 ± 40.5%) during single limb hop (p < 0.001). In the ACL(p < 0.001) and the NonACL (p < 0.001) limbs functional demand was lower while walking (ACL: 30.0 ± 12.7%; NonACL: 29.0 ± 10.9%) when compared to hopping. CONCLUSION: Our results revealed that functional demand increased as task difficulty increased, with both limbs using greater muscle capacity during hopping compared to walking. Our findings also support that the ACL limb uses less muscle capacity during hopping than the NonACL limb. The ACL limb may be impaired in its ability to use adequate muscle capacity to complete the task as demand increases. Supported by: NIH NICHD R01HD093626