Increase In Ground Reaction Force Research Articles

Dynamic Analysis of Upper- and Lower-Extremity Performance During Take-Offs and Landings in High-Wall Climbing: Effects of a Plyometric and Strength Training Intervention

This study used a 12-week plyometric and strength training program as an intervention to improve upper- and lower-extremity muscle strength for jumping and landing when climbing high walls. Sixty general non-athlete male college students were openly recruited and divided into an experimental group and a control group. The experimental group underwent a plyometric and strength training program twice a week for 12 weeks (24 sessions). The intervention was divided into three phases, each lasting four weeks, with the training intensity gradually increasing in each phase. A hand grip dynamometer was used to measure grip strength, and a PASCO double-track force plate was used to assess upper-extremity push-up force and lower-extremity take-off and landing strength. The results of the 12-week intervention showed that the experimental group experienced significant increases in grip strength (both hands), hand-ground reaction force, and upper-extremity hang time. Additionally, the time of upper-extremity action on the force plate decreased. Lower-extremity take-off strength improved, as reflected in increased ground reaction force, rate of force development, and passage time. Upon landing, ground reaction force decreased by 3.2%, and cushioning time shortened by 52.7%. This study concludes that plyometric and strength training have promising effects in enhancing upper- and lower-extremity strength, particularly in climbing and landing tasks.

Exploring the relationship between trunk muscles and lower limb injuries in Australian badminton players

Due to its dynamic nature, lower limb injuries are common in badminton. Overuse injuries of the knee, including tendon related conditions, are the most common. During jumping and landing, force transference and dissipation through the trunk is required, with the trunk muscles playing a vital role. However, the relationship between knee pain and the ability to voluntarily contract the trunk muscles has not yet been explored in badminton players. A cross-sectional study of Australian badminton players was therefore conducted. Players performed a single leg decline squat to identify those with knee pain. Ultrasound imaging was used to image and measure the size of the multifidus and quadratus lumborum, and the ability to contract the abdominal and multifidus muscles. Voluntary contraction of the trunk muscles was conducted with the subjects lying down. Independent samples T-Tests were performed to test for between group differences. Badminton players with knee pain had larger quadratus lumborum muscles and demonstrated a greater change in muscle thickness from the rested to contracted state. While we cannot comment on causation or direction, over co-contraction of trunk muscles has been shown in other studies to be associated with increased ground reaction forces on landing. Motor control training has been successfully used in other conditions to modify trunk muscle recruitment patterns and may therefore potentially represent a useful approach for badminton players.

Does carrying heavy loads impact ground reaction forces and plantar pressures in intervention police officers?

Background The main purpose of the study was to examine whether heavier loads might have an effect on ground reaction forces and plantar pressures. Methods Ninety-six elite intervention police officers were recruited in this cross-sectional study. Ground reaction forces and plantar pressures beneath the different foot regions were evaluated using Zebris FDM pressure platform, while a graduate increase in load carriage was as following: (i) ‘no load’, (ii) ‘a 5-kg load’, (iii) ‘a 25-kg load’ and (iv) ‘a 45-kg load’. Results Carrying heavier loads increased ground reaction forces beneath forefoot and hindfoot regions of both feet, and midfoot region for the right foot. For plantar pressures, increases beneath the hindfoot region of both feet and midfoot region of the right foot were observed, while carrying heavier loads. Conclusion This study shows significant increases in both ground reaction forces and plantar pressures, especially beneath the forefoot and hindfoot regions of both feet. Since the largest forces and pressures are produced beneath the hindfoot and forefoot, future research should pay special attention to these regions and their ground absorptions, additionally preventing from muscle and joint injuries.

The effect of carbon fiber plated shoes on submaximal running mechanics in non-elite runners

Running shoes constructed with midsole carbon fiber (CF) plates are often worn by elite long-distance runners and may result in mechanical and physiological changes (e.g. increased ground reaction forces, metabolic savings, and speed); however, the effect of these shoes is unknown in a non-elite population. We investigated biomechanical variables in non-elite runners running at submaximal speeds wearing the Nike ZoomX Vaporfly NEXT% 2 shoes (Next%), a shoe with CF plates and specialized energy-returning foam, compared to a shoe without CF plates (Pegasus). 12 male (20.75 ± 0.62 years) and 18 female (22.94 ± 5.06 years) runners were recruited. Following a warmup (400 m) in their own shoes at their preferred pace, runners ran 800 m twice, once in each shoe: Pegasus or Next%. Stride frequency during the shoe trials was controlled (via metronome) to preferred stride frequency recorded in the warmup. Wearable running analysis IMUs were worn to collect data. Stride length was significantly greater (p < 0.000) in Next% (2.97 ± 0.49 m) than in Pegasus (2.85 ± 0.46 m). Horizontal GRF was significantly higher (p = 0.009) in Next% (9.35 ± 1.92 N/kg/s) than in Pegasus (8.72 ± 1.41 N/kg/s). While wearing the Next% shoe, non-elite runners exhibited a significant increase in stride length and horizontal GRF while maintaining a constant stride frequency which ultimately resulted in an increase in running speed.

The effects of age and central field loss on maintaining balance control when stepping up to a new level under time-pressure.

To investigate the effects of age and central field loss on the landing mechanics and balance control when stepping up to a new level under time-pressure. Eight older individuals with age-related macular degeneration (AMD), eight visually normal older and eight visually normal younger individuals negotiated a floor-based obstacle followed by a 'step-up to a new level' task. The task was performed under (1) no-pressure; (2) time-pressure: an intermittent tone was played that increased in frequency and participants had to complete the task before the tone ceased. Landing mechanics and balance control for the step-up task was assessed with a floor-mounted force plate on the step. Increased ground reaction forces and loading rates were observed under time-pressure for young and older visual normals but not for AMD participants. Across conditions, loading rates and ground reaction forces were higher in young normals compared to older normals and AMD participants. Young visual normals also demonstrated 35-39% shorter double support times prior to and during the step-up compared to older normals and AMD participants. All groups shortened their double support times (31-40%) and single support times (7-9%) in the time-pressure compared to no-pressure condition. Regarding balance control, the centre-of-pressure displacement and velocity in the anterior-poster direction were increased under time-pressure for young and older visual normals but not for AMD participants. The centre-of-pressure displacement and velocity in the medial-lateral direction were decreased for the AMD participants under time-pressure but not for young and older visual normals. Despite walking faster, AMD participants did not adapt their landing mechanics under time-pressure (i.e., they remained more cautious), whilst older and young adults with normal vision demonstrated more forceful landing mechanics with the young being most forceful. A more controlled landing might be a safety strategy to maintain balance control during the step-up, especially in time-pressure conditions when balance control in the anterior-posterior direction is more challenged.

Ground reaction forces during double limb stances while walking in individuals with unilateral transfemoral amputation.

The asymmetrical gait of individuals with unilateral transfemoral amputation has been well documented. However, there is not a wealth of investigation into asymmetries during the double limb stance depending on whether the intact or prosthetic limb is leading. The first aim of this study was to compare ground reaction forces during the double limb stance of individuals with unilateral transfemoral amputation depending on whether their intact (initial double limb stance) or prosthetic (terminal double limb stance) limb was leading. The second aim of this study was to compare the asymmetry ratio of ground reaction forces during the double limb stance between individuals with and without unilateral transfemoral amputation. Thirty individuals, fifteen with unilateral transfemoral amputation and fifteen who were able-bodied, were recruited for this study. Each individual walked on an instrumented treadmill for 30s at eight different speeds, ranging from 2.0km/h to 5.5km/h with .5km/h increments. Ground reaction force parameters, temporal parameters, and asymmetry ratios of all parameters were computed from the data collected. The appropriate statistical analyses of all data based on normality were conducted to investigate the aims of this study. Significant main effects of speed, double limb stance, and their interactions were found for most parameters (p < .01 or p < .05). Individuals with unilateral transfemoral amputation spent a longer duration in terminal double limb stance than initial double limb stance at all tested speeds. They also experienced significantly higher peak vertical ground reaction force during initial double limb stance compared to terminal double limb stance with increasing walking speed. However, during terminal double limb stance, higher anteroposterior ground reaction force at initial contact was found when compared to initial double limb stance. Significant differences between individuals with unilateral transfemoral amputation and able-bodied individuals were found in asymmetry ratios for peak vertical ground reaction force, anteroposterior ground reaction force, anteroposterior shear, and mediolateral shear at all tested speeds. Asymmetrical loading persists in individuals with unilateral transfemoral amputation during double limb stance. Increasing walking speed increased ground reaction force loading asymmetries, which may make individuals with unilateral transfemoral amputation more susceptible to knee osteoarthritis or other musculoskeletal disorders. Further study is necessary to develop ideal gait strategies for the minimization of gait asymmetry in individuals with unilateral transfemoral amputation.

Effect of multi-component exercises program on pain-related gait adaptations among individuals with osteoarthritis of the knee joint.

Osteoarthritis of the knee causes pain and gait disturbances, as well as a distinct gait pattern. Patients with knee OA have decreased range of motion (ROM) and increased ground reaction force. OA reduces stride length and walking speed. To determine the effect of a multi-component exercise program on pain-related gait adaptations among individuals with osteoarthritis of the knee joint and to compare the effect of multi-component exercises with traditional exercises on pain-related gait adaptations among individuals with osteoarthritis of the knee joint. This was an experimental study done between 120 patients having knee OA, of both genders, and between the age group of 50-65 years. These individuals were residents of the city of Karad and they were randomly divided into group A (conventional/traditional) and group B (experimental). A pretest assessment was done and the treatment was given for 6 weeks. The later posttest assessment was done and further statistical tests like paired and unpaired t tests were used. Among the 120 subjects with OA knee, the age group of 60-65 years (44%) was found to be commonly affected. Thirty-nine were males (32.5%) and 81 were females (67.5%). Fifty-eight subjects (48%) were found to be commonly overweight. Thirty-two subjects (27%) had Genu Valgum deformity, and 88 subjects (73%) had Genu Varum deformity at the knee joint. The Pvalue within both group A and group B was found to be statistically significant for the entire outcome measures used for assessment. The pretest vs post test values of the WOMAC scale for patients with knee OA within both groups were found to be extremely significant (P < 0.0001). As for the MMT score in these patients, the Knee Flexors of Group A were not significant for right side (P = 0.7088) as well as for left side (P = 0.083) and in Group B they were extremely significant (P < 0.0001) for both sides. For the ROM scores within both groups, Knee Flexion of Group A for both sides was found to be extremely significant (P < 0.0001) for both sides. And for the pretest vs posttest values of within the groups'gait parameters among these patients with OA knees, for cadence both groups B were found to be extremely significant (P < 0.0001). The stride length for Group A was found to be very significant (P = 0.0060) and for Group B it was (P < 0.0001). Also, the P values of the various outcome measures between both groups were found to have statistical significance of their own. Effect of Multi-Component Exercise Program on Pain-Related Gait Adaptations Among Individuals with Osteoarthritis of the Knee joint was found to be significant in pain reduction, improving strength, range of motion, and the gait parameters such as an increase in cadence, stride length, step length and decrease in the step width.

How Different Load Carriage Scenarios Impact the Gait in Police Officers

The main purpose of this study was to examine the effects on gait of carrying different standardized police loads. In this cross-sectional study, we randomly recruited 30 special police officers. Spatiotemporal and kinetic gait changes were evaluated by using the Zebris FDM pressure platform, when load carriage ranged from 5 to 45 kg. Heavier loading conditions significantly increased ground reaction forces and plantar pressures for both feet beneath the forefoot, midfoot, and hindfoot regions of the foot. However, as load increased there were no significant changes in spatiotemporal gait parameters. This study shows that heavier loads carried by special police officers significantly increase ground reaction forces and plantar pressures under different foot regions. Thus, special interventions aiming to lower kinetic gait parameters throughout a different ergonomics and design of standardized equipment should be considered.

Altered mechanics and increased loading on intact limbs of individuals with a unilateral transtibial amputation in comparison with non-amputees during a start-stop task

Individuals with a unilateral transtibial amputation (ITTA) often experience greater loading on the intact limb during running and stepping tasks compared to individuals without amputation. This study aimed to investigate the mechanics of load absorption in the intact limb of ITTA and determine if increased ground reaction forces (GRF) persist during a start-stop task which (i) controlled touch-down velocity and (ii) removed the requirement for on-going locomotion. Data were collected using a twelve-camera motion capture system with two Kistler force platforms. Variables were extracted during the final loading phase of a 2-step start-stop task. The intact limb of ITTA and the dominant limb of able-bodied controls were compared using independent t-tests and effect size analysis. ITTA showed lower knee flexion angles at touchdown (p = 0.007, g = −1.43), and peak vertical GRF (p = 0.01, g = −1.33) compared to control subjects. ITTA also exhibited less hip (p = 0.14, g = 0.76) and ankle (p = 0.002, g = 1.82) absorptive power at touchdown and at peak vertical GRF (hip: p = 0.01, g = 1.23; ankle: p = 0.05, g = 0.97). ITTA exhibited greater peak vertical GRF (p = 0.01, g = 1.30) and braking GRF (p = 0.05, g = −0.96) on the intact limb compared to the controls. Our results indicate altered joint mechanics through the intact limb of ITTA are independent of the touchdown conditions or the need for ongoing locomotion. These altered joint mechanics increased loading experienced by the intact limb. Further work should be conducted examining a variety of other dynamic movements to fully understand the involved mechanics, so that intervention studies can be developed to reduce the load experienced by ITTA.

Biomechanics Differ for Individuals With Similar Self-Reported Characteristics of Patellofemoral Pain During a High-Demand Multiplanar Movement Task.

Patellofemoral pain (PFP) is often categorized by researchers and clinicians using subjective self-reported PFP characteristics; however, this practice might mask important differences in movement biomechanics between PFP patients. To determine whether biomechanical differences exist during a high-demand multiplanar movement task for PFP patients with similar self-reported PFP characteristics but different quadriceps activation levels. Cross-sectional design. Biomechanics laboratory. A total of 15 quadriceps deficient and 15 quadriceps functional (QF) PFP patients with similar self-reported PFP characteristics. In total, 5 trials of a high-demand multiplanar land, cut, and jump movement task were performed. Biomechanics were compared at each percentile of the ground contact phase of the movement task (α = .05) between the quadriceps deficient and QF groups. Biomechanical variables included (1)whole-body center of mass, trunk, hip, knee, and ankle kinematics; (2)hip, knee, and ankle kinetics; and (3)ground reaction forces. The QF patients exhibited increased ground reaction force, joint torque, and movement, relative to the quadriceps deficient patients. The QF patients exhibited: (1)up to 90, 60, and 35N more vertical, posterior, and medial ground reaction force at various times of the ground contact phase; (2)up to 4° more knee flexion during ground contact and up to 4° more plantarflexion and hip extension during the latter parts of ground contact; and (3)up to 26, 21, and 48 N·m more plantarflexion, knee extension, and hip extension torque, respectively, at various times of ground contact. PFP patients with similar self-reported PFP characteristics exhibit different movement biomechanics, and these differences depend upon quadriceps activation levels. These differences are important because movement biomechanics affect injury risk and athletic performance. In addition, these biomechanical differences indicate that different therapeutic interventions may be needed for PFP patients with similar self-reported PFP characteristics.

Center of Pressure, Vertical Ground Reaction Forces, and Neuromuscular Responses of Special-Forces Soldiers to 43-km Load Carriage in the Field.

The primary purpose of this study was to examine lateral deviations in center of pressure as a result of an extreme-duration load carriage task, with particular focus on heel contact. A total of 20 (n = 17 males and n = 3 females) soldiers from a special operation forces unit (body mass 80.72 [21.49]kg, stature 178.25 [8.75]cm, age 26 [9]y) underwent gait plantar pressure assessment and vertical jump testing before and after a 43-km load carriage event (duration 817.02 [32.66]min) carrying a total external load of 29.80 (1.05)kg. Vertical jump height decreased by 18.62% (16.85%) from 0.30 (0.08) to 0.24 (0.07) m, P < .001. Loading peak and midstance force minimum were significantly increased after load carriage (2.59 [0.51] vs 2.81 [0.61] body weight, P = .035, Glass delta = 0.44 and 1.28 [0.40] vs 1.46 [0.41] body weight, P = .015, Glass delta = 0.45, respectively) and increases in lateral center of pressure displacement were observed as a result of the load carriage task 14.64 (3.62) to 16.97 (3.94)mm, P < .029. In conclusion, load carriage instigated a decrease in neuromuscular function alongside increases in ground reaction forces associated with injury risk and center of pressure changes associated with ankle sprain risk. Practitioners should consider that possible reductions in ankle stability remain once load carriage has been completed, suggesting soldiers are still at increased risk of injury even once the load has been removed.

Walking With Ears: Altered Auditory Feedback Impacts Gait Step Length in Older Adults.

Auditory feedback may provide the nervous system with valuable temporal (e. g., footstep sounds) and spatial (e.g., external reference sounds) information that can assist in the control of upright walking. As such, hearing loss may directly contribute to declines in mobility among older adults. Our purpose was to examine the impact of auditory feedback on the control of walking in older adults. Twenty older adults (65–86 years) with no diagnosed hearing loss walked on a treadmill for three sound conditions: Baseline, Ear Plugs, and White Noise. We hypothesized that in response to reduced temporal auditory feedback during the Ear Plugs and White Noise conditions, participants would adapt shorter and faster steps that are traditionally believed to increase mechanical stability. This hypothesis was not supported. Interestingly, we observed increases in step length (p = 0.047) and step time (p = 0.026) during the Ear Plugs condition vs. Baseline. Taking longer steps during the Ear Plugs condition may have increased ground reaction forces, thus allowing participants to sense footsteps via an occlusion effect. As a follow-up, we performed a Pearson's correlation relating the step length increase during the Ear Plugs condition to participants' scores on a clinical walking balance test, the Functional Gait Assessment. We found a moderate negative relationship (rho = −0.44, p = 0.055), indicating that participants with worse balance made the greatest increases in step length during the Ear Plugs condition. This trend suggests that participants may have actively sought auditory feedback with longer steps, sacrificing a more mechanically stable stepping pattern. We also hypothesized that reduced spatial localization feedback during the Ear Plugs and White Noise conditions would decrease control of center of mass (COM) dynamics, resulting in an increase in lateral COM excursion, lateral margin of stability, and maximum Lyapunov exponent. However, we found no main effects of auditory feedback on these metrics (p = 0.580, p = 0.896, and p = 0.056, respectively). Overall, these results suggest that during a steady-state walking task, healthy older adults can maintain walking control without auditory feedback. However, increases in step length observed during the Ear Plugs condition suggest that temporal auditory cues provide locomotor feedback that becomes increasingly valuable as balance deteriorates with age.

The effects of military style ruck marching on lower extremity loading and muscular, physiological and perceived exertion in ROTC cadets

Military ruck marching with load carriage increases ground reaction forces, which are related to bone stress injuries (BSI). This study’s purpose was to examine whether a ruck march increases impact loading and to describe muscular, physiological and perceived exertion in Army Reserve Officer Training Corps (ROTC) cadets. Secondary purposes examined relationships among loading changes after the ruck march and baseline characteristics. Fifteen Army ROTC cadets performed a 4-mile march. Lower extremity loading and muscular, physiological and perceived exertion were measured pre- and post-march. Results indicated significant increases in peak impact force and loading rate and decreases in ankle dorsiflexion and plantarflexion strength. Factors that might have been related to changes seen in lower extremity loading did not yield any compelling relationships to explain those changes. In conclusion, the ruck march led to increased peak impact force and loading rate, which have been shown to be related to the risk of BSI. Practitioner summary: This study examined ROTC cadets ankle strength and lower extremity loading before and after a ruck march. We found that lower extremity loading increased after the march, and ankle dorsiflexion (DF) strength decreased, despite the cadets not feeling fatigued. These changes are consistent with risk factors for bone stress injuries. Abbreviations: BSI: bone stress injury; ROTC: Reserve Officer Training Corps; PIF: peak impact force; LR: loading rate; RPE: rate of perceived exertion; APFT: Army physical fitness test; DF: dorsiflexors; PF: plantar-flexors; INV: invertors; EV: evertors; HHD: handheld dynamometer; %HRmax: percentage of maximum heart rate

Effects of kettlebell mass on lower-body joint kinetics during a kettlebell swing exercise

ABSTRACT Functional training aims to provide specific adaptations due to exercise training and utilises a variety of equipment, including kettlebells. Due to the training principle of overload, a greater resistance must be applied to yield increased strength results. This study examined the effects of kettlebell mass on lower body joint kinetics in young recreationally trained adults. Thirty recreationally active, college-aged adults were recruited for this study. Participants performed hip-hinge style swings with kettlebells equivalent to 10%, 15% and 20% of their respective body mass. 3-D marker coordinate data were captured via infrared camera system and ground reaction force data were measured with two force plates. The resultant joint moments of the lower body were calculated using the inverse dynamics procedure. As mass increased, there was an increase in joint moment at the L4/5, hip and ankle joint, primarily due to an increase in ground reaction force. Increasing kettlebell mass can potentially cause greater strength gains in the hip and trunk musculature due to increase in lower body moments, while avoiding excessive moments about the knee.

Ground reaction forces don’t indicate tibial forces: implications for injury prevention, shoe design & wearable tech

Tibial stress fractures are a common overuse injury due to repeated bone loading. More than 50 scientific publications per year interpret increase in ground reaction force (GRF) metrics (e.g. impac...

Increased Ground Reaction Force Load Rates In Runners With Active Patellofemoral Pain

Increased vertical ground reaction force load rates have been associated with running injuries, and specifically with tibial stress fractures and plantar fasciitis. Inconsistent findings have been reported regarding the role of load rates in runners with patellofemoral pain (PFP), one of the most common injuries in runners. Limited studies in this patient population have been performed and prior investigators did not examine components of load rates beyond the vertical component. PURPOSE: To compare vertical, resultant, posterior, medial and lateral load rates, and peak vertical forces in runners with active PFP to healthy controls. METHODS: 30 runners with active PFP (16F, 14M, 40.2±12.8 yrs, 67.5±10.0 kg) and 30 healthy controls (CON) (18F, 12M, 34.8±10.9 yrs, 70.4±14.0 kg), all habitual rearfoot strikers, completed an instrumented treadmill assessment at a self-selected speed. Controls were matched for speed (PFP=2.50 m/s, CON=2.51 m/s). Load rates (vertical average and instantaneous (VALR, VILR), resultant instantaneous (RILR), posterior instantaneous (PILR), medial instantaneous (MILR) and lateral instantaneous (LILR)) over the first 25% of stance and normalized to bodyweights. Peak vertical ground reaction forces (vGRF) were calculated over all of stance. Values were averaged across 10 consecutive strides. The injured leg was analyzed for the PFP group, and the right/left leg was randomly selected and counterbalanced for CON. RESULTS: Runners in the PFP group showed significantly higher mean VALR (p=0.036, d=0.56), VILR (p= 0.040, d=0.54) and RILR (p=0.036, d=0.55) than CON. No differences were found in PILR (p=0.668), MILR (p=0.193), and LIRL (p=0.367) (Figure 1), or in peak vGRF (Mean difference=0.03 BW, p=0.458). CONCLUSION: Runners with active PFP exhibit higher vertical and resultant load rates.Figure 1: Mean load rates between patellofemoral pain and control groups-VALR, VILR, RILR plotted on left axis; PILR, MILR, and LILR plotted on right

Mechanical Loading of the Femoral Neck in Human Locomotion.

Advancing age and reduced loading are associated with a reduction in bone formation. Conversely, loading increases periosteal apposition and may reduce remodeling imbalance and slow age-related bone loss, an important outcome for the proximal femur, which is a common site of fracture. The ability to take advantage of bone's adaptive response to increase bone strength has been hampered by a lack of knowledge of which exercises and specific leg muscles load the superior femoral neck: a common region of microcrack initiation and progression following a sideways fall. We used an in vivo method of quantifying focal strains within the femoral neck in postmenopausal women during walking, stair ambulation, and jumping. Relative to walking, stair ambulation and jumping induced significantly higher strains in the anterior and superior aspects of the femoral neck, common regions of microcrack initiation and progression following a fall. The gluteus maximus, a hip extensor muscle, induced strains in the femoral neck during stair ambulation and jumping, in contrast to walking which induced strains via the iliopsoas, a hip flexor. The ground reaction force was closely associated with the level of strain during each task, providing a surrogate indicator of the potential for a given exercise to load the femoral neck. The gluteal muscles combined with an increased ground reaction force relative to walking induce high focal strains within the anterosuperior region of the femoral neck and therefore provide a target for exercise regimens designed to slow bone loss and maintain or improve microstructural strength. Model files used for calculating femoral neck strains are available at uitbl.mechse.illinois.edu/downloads © 2018 American Society for Bone and Mineral Research.

Physical and Performance Characteristics Related to Unintentional Musculoskeletal Injury in Special Forces Operators: A Prospective Analysis.

Seventy-seven percent of musculoskeletal injuries sustained by United States Army Special Forces Operators are preventable. Identification of predictive characteristics will promote the development of screening methods to augment injury-prevention programs. To determine physical and performance characteristics that predict musculoskeletal injuries. Clinical laboratory. A total of 95 Operators (age = 32.7 ± 5.1 years, height = 179.8 ± 6.9 cm, mass = 89.9 ± 12.7 kg). Laboratory testing consisted of body composition, aerobic and anaerobic capacity, upper and lower body strength and flexibility, balance, and biomechanical evaluation. Injury data were captured for 12 months after laboratory testing. Injury frequencies, cross-tabulations, and relative risks (RRs) were calculated to evaluate the relationships between physical characteristics and injury proportions. Between-groups differences (injured versus uninjured) were assessed using appropriate t tests or Mann-Whitney U tests. Less shoulder-retraction strength (RR = 1.741 [95% confidence interval = 1.003, 3.021]), knee-extension strength (RR = 2.029 [95% confidence interval = 1.011, 4.075]), and a smaller trunk extension : flexion ratio (RR = 0.533 [95% confidence interval = 0.341, 0.831]) were significant risk factors for injury. Group comparisons showed less trunk strength (extension: P = .036, flexion: P = .048) and smaller right vertical ground reaction forces during landing ( P = .025) in injured Operators. Knee strength, aerobic capacity, and body mass index were less in the subgroup of spine-injured versus uninjured Operators ( P values = .013-.036). Knee-extension and shoulder-retraction strength were risk factors for musculoskeletal injury in Operators. Less trunk-flexion and -extension strength, higher body mass index, lower aerobic capacity, and increased ground reaction forces during landing were characteristics that may also contribute to musculoskeletal injury. Having 2 or more risk factors resulted in a greater injury proportion (χ2 = 13.512, P = .015); however, more research is needed. Athletic trainers working in the military or similar high-demand settings can use these data to augment screening and injury-prevention protocols.

Sensitivity of biomechanical outcomes to independent variations of hindfoot and forefoot stiffness in foot prostheses

Many studies have reported the effects of different foot prostheses on gait, but most results cannot be generalized because the prostheses’ properties are seldom reported. We varied hindfoot and forefoot stiffness in an experimental foot prosthesis, in increments of 15N/mm, and tested the parametric effects of these variations on treadmill walking in unilateral transtibial amputees, at speeds from 0.7 to 1.5m/s. We computed outcomes such as prosthesis energy return, center of mass (COM) mechanics, ground reaction forces, and joint mechanics, and computed their sensitivity to component stiffness. A stiffer hindfoot led to reduced prosthesis energy return, increased ground reaction force (GRF) loading rate, and greater stance-phase knee flexion and knee extensor moment. A stiffer forefoot resulted in reduced prosthetic-side ankle push-off and COM push-off work, and increased knee extension and knee flexor moment in late stance. The sensitivity parameters obtained from these tests may be useful in clinical prescription and further research into compensatory mechanisms of joint function.

The effect of leg compliance in multi-directional jumping of a flea-inspired mechanism

Inspired by the relationship between leg compliance and jumping performance in the false stick insect, this paper describes how variations in leg compliance and jumping direction affect the performance of a flea-inspired jumping mechanism. The amount of energy lost during jumping was determined by examining the ratio of kinetic energy to input energy (also called conversion efficiency). Leg compliance is modeled based on the compliant mechanics to determine energy transfer during jumping and determined the optimum degree of leg compliance for maximizing performance. Jumping experiments are then performed using six different legs with progressively greater degrees of stiffness and three different jumping directions. The experiments show that conversion efficiency decreases by approximately 3–5% as leg stiffness increases, compared to the optimal case. In the most compliant legs (i.e. stiffness of 0.0338 Nm rad−1 or less), conversion efficiency rapidly drops to near 0% because the leg bends so much that it cannot support the thrusting force. The optimal conversion efficiency tends to increase when the mechanism jumps vertically owing to reduced slippage and increased ground reaction force. These investigations show that optimizing leg compliance can improve the performance of a jumping robot by up to 5% by enabling more of the initially stored energy in the leg to be used. This finding will likely prove helpful for choosing the leg stiffness for a small-scale jumping robot.