LE3 .A278 2018

2018

Landry, Scott

Acadia University

Bachelor of Science

Honours

Biology

Biology

Anterior Cruciate Ligament (ACL) injuries represent some of the most frequent and detrimental sporting injuries of the lower extremities. The ACL passively resists anterior tibial translation and stabilizes the knee during internal/external and varus/valgus moments. Non-contact ACL injuries, those which do not involve a direct blow to the knee, account for upward of 70% of all ACL injuries. Furthermore, females are 2-8 times more likely to sustain a non-contact ACL injury after the onset of puberty, making the identification of risk factors imperative to mitigating the devastating effects of this injury. The present study examined the effect of sex and age (pre-pubescent versus post-pubescent) on muscle co-contraction patterns during the first and second landing phases of double leg drop jumps, a maneuver which puts athletes at risk of injury. A comprehensive protocol developed within the John MacIntyre motion Laboratory of Applied Biomechanics enabled longitudinal data to be collected for the purpose of identifying non-contact ACL injury risk factors. Different neuromuscular co-contraction patterns at the knee joint may jeopardize the stability of the knee and thereby put the ACL at risk of injury. Recent research has focused on the role that co-contraction of the hamstring and gastrocnemius muscles with the quadriceps may have on the stability of the knee during dynamic movement. Specifically, decreased hamstring activation and increased gastrocnemius activation at small knee flexion angles during jump landings have been noted to increase the risk of lower body injury. Elite level athletes (males n=49, females n=54) recruited from Acadia’s varsity programs and local youth sport organizations participated in this study. Of the males, 27 were categorized as pre-pubescent (age = 10.56 years ±1.85) and 22 post-pubescent (age = 20.77 years ±2.43). Likewise, 25 females were categorized as pre-pubescent (age = 10.72 years ±1.28) and 29 post pubescent (age = 20.07 years ±1.31). A double leg drop jump protocol was used to calculate pre and post contact landing phase co-contraction index (CCI) values between the quadriceps (vastus lateralis (VL), and the vastus medialis (VM)), the hamstrings (biceps femoris or lateral hamstring (LH), and the emitendinosus / semimem branosus or medial hamstring (MH)), and the gastrocnemii (medial head of the gastrocnemius (MG), and the lateral head of the gastrocnemius (LG)) using a 16 channel wireless electromyography system and 3 force plates. A 2-way between subjects ANOVA was used to test for age (pre-pubescent versus post-pubescent), sex (male versus female) or interaction effects on the CCI values between the quadriceps-hamstring medial and lateral pairings and between the quadriceps-gastrocnemii medial and lateral pairings for the dominant leg. The results of this study demonstrated that compared to pre-pubescent athletes, post-pubescent athletes exhibited smaller CCI values both medially and laterally during the two pre-landing phases. It was also observed that post-pubescent athletes exhibit greater CCI values for the LG and VL paring during the first post-landing phase. Females also exhibited greater MH and VM activation during the first pre-landing phase of the double leg drop jumps. These findings provide insight into the influence that co-contraction, preparatory activation, and differing jumping phases may have as risk factors for non-contact ACL injuries in pre-and post-pubescent athletes. In addition, it is suggested that building on the present findings may help determine when the optimal time is to start implementing injury prevention programs focused on sex and age.

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https://scholar.acadiau.ca/islandora/object/theses:2649