Speed and Terrain Impact Ground Reaction Forces During Load Carriage

Load carriage leads to larger, faster vertical ground reaction forces (GRFs), and greater risk of musculoskeletal injury. Although increased lower limb flexion can help dissipate the vertical GRF, reducing injury risk, it is unclear if terrain affects limb flexion and vertical GRFs during load carriage. This study quantified lower limb biomechanics as participants walked, jogged and ran with heavy body borne load over different terrain. We hypothesize that participants will decrease lower limb flexion, but increase peak vertical GRFs as speed increases, but these changes will vary with terrain. Each participant walked (1.3 m/s), jogged (3.0 m/s) and ran (4.5 m/s) with body borne load (15 kg) over a rocky, firm, soft, and flat terrain. During each locomotor task, peak vertical GRF and range of hip, knee and ankle motion (ROM) were calculated, and submitted to statistical analysis. Significant speed by surface interactions were evident for peak vertical GRF (p \u3c 0.001), and ankle and knee ROM (p=0.030 and p \u3c 0.001). Speed impacted peak vertical GRF, and ankle and knee ROM (all: p \u3c 0.001), where GRF and ankle were larger, but knee motion smaller during the run. Surface impacted peak vertical GRF and ankle ROM (p \u3c 0.001 and p=0.008). Unexpectedly, participants decreased peak vertical GRF on the rocky compared to all other surfaces. Through the use of this study, training programs can be adapted to help athletes and military personnel decrease their risk of injury while training

Impact of Knee Injury and Disease on Frontal Plane Knee Biomechanics During Walk on Uneven Surfaces

Frontal plane knee biomechanics, in particular speed and magnitude of knee adduction motion, are implicated in knee osteoarthritis development. Although individuals are between 50% to 90% more likely to develop knee osteoarthritis after anterior cruciate ligament reconstruction (ACL-R), it is unknown if ACL-R individuals exhibit knee adduction biomechanics related to OA development. This study sought to quantify speed and magnitude of knee adduction for knee OA and ACL-R individuals. We hypothesize that OA will exhibit larger, faster knee adduction biomechanics than ACL-R, which will increase at great walk speed and over a challenging surface. Six individuals with ACL-R and 8 individuals with knee OA had knee adduction quantified as they walked 1.3 m/s and at a self-selected speed over a flat and an uneven surface. Peak of stance, and average and maximum velocity of knee adduction joint angle and moment between heel strike and peak of stance were submitted to repeated measures ANOVA to compare main and interaction effects between group, speed and surface. There was a walk speed by group interaction for peak knee adduction moment (p = 0.048). Walk speed impacted maximum knee adduction joint angle (p=0.004) and moment velocity (p=0.041), while surface impacted peak knee adduction joint angle (p=0.035) and maximum knee adduction joint moment velocity (p=0.007). In partial agreement with our hypothesis, speed and magnitude knee adduction biomechanics increased with walk speed and surface, but OA did not consistently exhibit larger knee adduction biomechanics than ACL-R

Stiffness of Peroneal Musculature Relates to Ankle Inversion

Adequate stiffness of the peroneal musculature may prevent excessive ankle inversion that leads to injury. Thus, this study determined the relation between peroneal stiffness and ankle inversion. Ten (9 male and 1 female) participants (ht: 1.7 0.1 m, wt: 73.3 9.8 kg) had ankle inversion (including range of inversion and time to peak inversion) quantified during a sudden inversion event. Resting and contracted peroneal muscle stiffness was also quantified with an ultrasound using shear wave elastography. Correlations examined linear relationship between ankle inversion and muscle stiffness. Resting muscle stiffness exhibited a positive relationship with the range of ankle inversion (r = 0.508) and contracted muscle stiffness exhibited a negative relationship with time to peak inversion (r = -0.538), but neither was significant (p = 0.067 and p = 0.054). Both resting and contracted stiffness of the peroneals were related to ankle inversion. But, more work is needed to determine the stiffness necessary to prevent the excessive inversion that leads to injury

Age Impacts Lower Limb Stiffness During Distracted Negotiation of Slick Stairs

Older adults (OA, over 65 years) typically use compensatory gait strategies for safe stair descent. Adequate lower limb stiffness, including leg and individual joint (i.e., hip, knee, and ankle), may be necessary to prevent falling, particularly when negotiating a slick surface or when the individual is distracted. Yet, it is unknown if OA change lower limb stiffness for safe stair descent during these challenging situations. Thus, 13 young adults (YA, between 18-25 years) and 12 OA had leg and lower limb joint stiffness quantified during a stair descent (18.5 cm rise). Each participant performed the stair descent on normal and slick surfaces, and with and without cognitive distraction. Leg stiffness (quantified as change in leg length when ground reaction force is applied) and hip, knee and ankle joint stiffness (calculated as change in joint angle when a joint moment is applied) were submitted to 3-way mixed model ANOVA. 3-way interaction for ankle stiffness (p = 0.036) was observed. Without a distraction, the YA exhibited a stiffer ankle on the normal compared to slick surface (p = 0.007), but YA did not change ankle stiffness when distracted (p = 0.125). Neither distraction, nor surface impacted OA ankle stiffness (p \u3e 0.05). YA exhibited a stiffer hip than OA (p = 0.009), and all participants increased hip stiffness on the slick surface (p = .001). Leg and knee stiffness did not differ by age, or change with surface or distraction (p \u3e 0.05). YA may possess the neuromuscular function to increase hip and ankle stiffness during stair descent. Future work is needed to determine whether OA changes in lower limb stiffness are an attempt to prevent accidental fall or from compromised muscular function

Relationship Between Peroneal Muscle Architecture and Dynamic Ankle Function for Individuals with Chronic Ankle Instability

Peroneal architecture may predispose individuals to the impaired ankle function that leads to chronic ankle instability (CAI). But, it is unclear if CAI individuals exhibit different peroneal and ankle function than healthy controls. This study determined peroneal muscle architecture and dynamic ankle function for 30 (12 CAI, 18 CON) participants. Each participant had peroneal architecture (physiological cross-sectional area (PCSA), volume, stiffness), ankle strength (both maximum dorsiflexion and eversion), and ankle biomechanics (peak plantarflexion and negative ankle work during a 30 cm drop landing) quantified. Each variable was submitted to independent t-tests to determine group differences and linear discriminant analysis to determine whether peroneal architecture and dynamic ankle function could accurately identify CAI status. CAI individuals exhibited weaker dorsiflexors (p=0.049), but no differences in peroneal architecture (PCSA p=0.546, volume p=0.488, stiffness p=0.653) or ankle function (negative work p=0.383, peak plantarflexion rotation p=0.958). Yet, 75% (9/12) of CAI and 66.7% (12/18) of CON participants were accurately identified from peroneal muscle architecture and dynamic ankle function. Considering 75% of CAI individuals were accurately identified, specific peroneal and ankle function measures may predispose individuals to CAI

Load and Sex Impact Lower Limb Muscle Volume During Running

Military training requires personnel to safely dissipate large ground reaction forces to avert musculoskeletal injury. Training often requires running with heavy body borne loads, but it is currently unknown if active lower limb muscle volume increases when running with load, and whether muscle volume differs between sexes. Thirty-six (20 Male, 16 Female) participants had lower limb muscle volume quantified when running 4.0 m/s with four body borne loads (20, 25, 30, 35 kg). Custom Matlab code calculated hip, knee, and ankle muscle force (Fm=Mjoint/r) and volume (Vm = L×Fm/σ), using moment arm (r), fascicle length (L) and isometric muscle force per unit of cross-sectional area (σ=20N/cm2) data obtained from published work. Muscle volume was submitted to an RM ANOVA to test the main effect and interaction between sex (male, female) and load (20, 25, 30, 35 kg). Alpha was p \u3c 0.05. Females used greater knee muscle volume than males to run with the 20 (p=0.019) and 35 kg (p=0.017), but not 25 (p=0.280) or 30 kg (p=0.534) loads. Load increased active muscle volume increased at the ankle (p=0.012), but not hip (p=0.112) or knee (p=0.887). Sex had no effect on active muscle volume (p\u3e0.05)

Median Frequency Shift of EMG During Prolonged Load Carriage

Musculoskeletal injuries can result from muscular fatigue common during military training. It is currently unknown how carrying military-relevant heavy body borne loads fatigue lower limb muscles during prolonged walking. Four (3 male, 1 female) participants had activation of eight dominant lower limb muscles (Tibialis Anterior, Lateral Gastrocnemius, Rectus Femoris, Vastus Lateralis, Lateral Hamstring, Gluteus Medius, Rectus Abdominis, Erector Spinae) quantified when walking at 3.0m/s for 60 minutes with three body borne loads (0, 15, and 30 kg). At minute 0, 30, and 60 of the walking task, activation of each muscle was recorded with electromyography (EMG), and median frequency shift (MFS) of the signal calculated with custom Matlab code. Then, MFS for each muscle was submitted to a RM ANOVA to test the main and interaction effects of time (0, 30, and 60 minutes) and load (0, 15, 30kg), with alpha p\u3c0.05. The addition of load reduced MFS for the lateral gastrocnemius (p=0.031), but had no significant effect on any other muscle (p\u3e0.05). Time had no significant effect on MFS for any muscle (p\u3e0.05). With a larger sample, we hypothesize both load and time will impact MFS of lower limb muscles, particularly those responsible for forward propulsion and weight acceptance

Surface, but Not Age Impacts Lower Limb Joint Work During Stair Ascent

Introduction: Age-related loss in lower limb strength, particularly at the ankle, may impair older adults (over 65 years of age) mobility, and result in biomechanical deficits compared to their younger counterparts. Older adults tend to walk slower with shorter steps and exhibit diminished ankle joint kinetics (i.e., moment, power and work) while walking and stepping up. Although the compromised ankle function leads older adults to produce smaller ankle joint torques and power output, reducing forces to propel the center of mass forward, it is unclear if they redistributed, or increase hip or knee work to safely walk, particularly when challenged with an uneven or slick surface. Objective: To compare positive lower limb work for young and older adults when walking over and stepping up with challenging surfaces, and determine whether redistributed power output. Methods: Twenty-eight (16 young, 18 to 25 years and 12 older, over 65 years) adults had positive work in the lower limb quantified when walking and stepping up at a self-selected speed over three surfaces (normal, uneven, and slick). Total limb, hip, knee and ankle positive work, and relative effort (% of total) at each joint were submitted to RM ANOVA to test main effect and interaction between surface (normal, uneven, and slick) and age (young and older adults). Results: Surface, but not age impact positive lower limb work. Surface impacted total limb (p=0.000), hip (p=0.007) and knee (p=0.001) positive work. The limb and knee produced more positive work on the uneven compared normal (