LE3 .A278 2020

2020

Lattimer, Lauren

Acadia University

Bachelor of Kinesiology

Honours

Kinesiology

Kinesiology

Introduction: Anterior cruciate ligament (ACL) injuries often occur during the deceleration phase of movement where the knee is close to full extension. In the sagittal plane, females tend to land with reduced hip and knee flexion. Neuromuscular fatigue has been hypothesized to cause injury to the lower extremity, particularly to the ACL. A common observation during fatiguing contractions is that activation of antagonist muscles increases progressively, which reduces the net torque the agonist can produce. During the stance phase of landing, hip extensor and knee flexor muscles contract eccentrically to counteract the external hip and knee flexion moments. Rationale: Weakness of the hip extensors results in altered landing strategies where females rely on the quadriceps to help with joint stability. Decreased hip flexion has been associated with higher knee extensor moments and females tend to have greater knee extensor moments and decreased hip extensor moments compared to men. Decreased torque producing ability of the hip extensors and knee flexors could further highlight sex differences. The purpose of this study was to investigate kinematics following neuromuscular fatigue and determine if sex differences exist in sagittal plane joint movements. Methods: Nine female (mean age 22.3 ± 3.4 years) and seven male (mean age 21.3 ± 2.6 years) participants completed a series of hop tests including the triple hop for distance (THop) and single leg drop jumps (SJump) pre and post-fatigue protocol. A 3D motion capture system was used to measure hip and knee kinematics for single leg tasks at IC, MAX and MEAN angles during the stance phase of landing and were compared pre and post fatigue. Surface EMG sensors were applied to various muscles of the lower limb and measured muscular activity during the stance phase and muscular activity at IC. The fatigue protocol consisted of consecutive effort to failure eccentric knee extensions and eccentric and concentric hip extensions. Separate two-way repeated measure MANOVAs were used to identify sex and time differences in lower extremity kinematics and muscular activation patterns. Results: Through kinematic analysis, findings include significant effects of fatigue on hip flexion angles (p=0.01), and knee flexion angles (p=0.039) during the THop test. There was a significant effect of sex found during hip flexion angles (p=0.033). A significant interaction effect of fatigue and sex on hip flexion angular velocity was seen during the SJump (p=0.03). Males experienced greater knee flexion angular velocities post-fatigue, whereas, females experienced a decrease in hip flexion angular velocities. In terms of muscle activity, significant findings were found for the GM and the ES. A significant sex effect was found during the THop for GM (p=0.053). A significant interaction effect of time and sex was seen in ES activation during the THop (p=0.023). Males had greater activation of the ES post-fatigue, whereas females had greater activation of the GM post-fatigue. Discussion: Landing with decreased hip and knee flexion angles increases the risk of injury to the ACL. By examining kinematic and muscle activation patterns, sex differences pertaining to injuries were observed. Following fatigue, females decreased flexion at the hip and knee. This suggests that fatigue of the lower limb decelerators causes females to land in positions which mimic those that cause ACL injury, which in turn heightens their risk of injury. The muscular activity results support these findings, as females experienced increased activation of the GM post-fatigue. Since the GM is a hip extensor, it prevents females from being able to adequately flex at the hip upon landings. Importance: Fatigue had a larger impact on female landing kinematics compared to males, highlighting fatigue of the posterior chain musculature as a potential risk factor for lower extremity injury. These findings could be applied in both rehabilitative and injury prevention settings.

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https://scholar.acadiau.ca/islandora/object/theses:3377