Date Published: February 6, 2019
Publisher: Public Library of Science
Author(s): Kayla D. Seymore, AuraLea C. Fain, Nicholas J. Lobb, Tyler N. Brown, Tiago M. Barbosa.
Increasing lower limb flexion may reduce risk of musculoskeletal injury for military personnel during landing. This study compared lower limb biomechanics between sexes and limbs when using normal and greater lower limb flexion to land with body borne load. Thirty-three participants (21 male, 12 female, age: 21.6±2.5 years, height: 1.7±0.1 m, weight: 74.5±9.0 kg) performed normal and flexed lower limb landings with four body borne loads: 20, 25, 30 and 35 kg. Hip and knee biomechanics, peak vertical ground reaction force (GRF), and the magnitude and direction of the GRF vector in frontal plane were submitted to two separate repeated measures ANOVAs to test the main and interaction effects of sex, load, and landing, as well as limb, load, and landing. Participants increased GRFs (between 5 and 10%) and hip and knee flexion moments when landing with body borne load, but decreased vertical GRF 19% and hip adduction and knee abduction joint range of motion and moments during the flexed landings. Both females and the non-dominant limb presented greater risk of musculoskeletal injury during landing. Females exhibited larger GRFs, increased hip adduction range of motion, and greater knee abduction moments compared to males. Whereas, the non-dominant limb increased knee abduction moments and exhibited a more laterally-directed frontal plane GRF vector compared to the dominant limb during the loaded landings. Yet, increasing lower limb flexion during landing does not appear to produce similar reductions in lower limb biomechanics related to injury risk for both females and the non-dominant limb during landing.
Lower limb musculoskeletal injury is a serious health concern for military personnel . According to the U.S. Army, an estimated 75% of recruits will sustain a musculoskeletal injury during basic and/or advanced training . These training-related injuries result in long-term disability and attrition, with substantial financial cost to the Armed Services [1,3]. The most common location of these musculoskeletal injuries is reportedly the knee joint . Recruits frequently suffer bony disorders and sprain, strain, or rupture of the knee’s soft-tissue during military training. These injuries often occur when the joint is forced into dynamic valgus [5,6] during the cutting and landing maneuvers common to military training . Dynamic valgus, described as excessive hip adduction, knee abduction, and ankle eversion joint motions and loads [8,9], may be potentially hazardous for military personnel because of the heavy body borne load they are required to don during training activities. These heavy body borne loads, which routinely range from 20 kg to 45 kg during training-related activities , reportedly alter a soldier’s hip and knee biomechanics [11–13], increasing their risk of suffering a musculoskeletal injury —particularly at the knee.
Significant interactions and main effects for sex, limb, load and landing are presented below. Because the interactions between and main effects of load and landing are redundant between ANOVAs, only the findings for load and landing type from the analysis for purpose 1 are presented below.
Landing with body borne load may increase risk of musculoskeletal injury [11,12]. In agreement with previous research, participants exhibited a significant 5 to 10% increase in peak vGRF when landing with each addition of body borne load . Dissipating these large landing forces can strain musculature surrounding a joint, particularly at the knee . The current participants exhibited a significant increase in hip and knee flexion joint moments with the addition of body borne load. Larger knee flexion moments are reported to be an indicator of knee soft-tissue loading , particularly with an extended limb. Participants were only able to achieve a greater knee flexion range of motion during landing with one of the lighter (25 kg) body borne loads, and exhibited no significant change in hip flexion range of motion with load. When landing with heavy body borne loads, an extended lower limb posture may prevent collapse of the lower limb , but may also result in greater transmission of the GRFs to the musculoskeletal system, increasing risk of injury . Future work is warranted to address how adaptations of other lower limb biomechanics, at the hip and ankle, impact knee biomechanics and risk of injury at the joint during dynamic tasks, particularly with the addition of heavy body borne loads common to military training.
Landing with body borne load increased participants’ risk of musculoskeletal injury. Specifically, participants exhibited greater GRFs and hip and knee joint moments with the addition of body borne load during landing. Increasing lower limb flexion during landing may decrease this risk of musculoskeletal injury, as participants were able to decrease GRFs and hip and knee biomechanics related to knee injury during the flexed landings. Both females and the non-dominant limb may be at greater risk of suffering a musculoskeletal injury during landing. Females exhibited larger GRFs, increased hip adduction range of motion, and greater knee abduction moments compared to males. Whereas, the non-dominant limb increased knee abduction moments and exhibited a more laterally-directed frontal plane GRF vector compared to the dominant limb during the loaded landings. Yet, increasing lower limb flexion landings does not appear to produce similar reductions in lower limb biomechanics related to injury risk for both females and the non-dominant limb during landing.