Propulsive Ground Reaction Forces Research Articles

Force-Time Characteristics of Repeated Bouts of Depth Jumps and the Effects of Compression Garments.

No studies have reported ground reaction force (GRF) profiles of the repeated depth jump (DJ) protocols commonly used to study exercise-induced muscle damage. Furthermore, while compression garments (CG) may accelerate recovery from exercise-induced muscle damage, any effects on the repeated bout effect are unknown. Therefore, we investigated the GRF profiles of 2 repeated bouts of damage-inducing DJs and the effects of wearing CG for recovery. Nonresistance-trained males randomly received CG (n = 9) or placebo (n = 8) for 72hours recovery, following 20 × 20m sprints and 10 × 10 DJs from 0.6m. Exercise was repeated after 14days. Using a 3-way (set × bout × group) design, changes in GRF were assessed with analysis of variance and statistical parametric mapping. Jump height, reactive strength, peak, and mean propulsive forces declined between sets (P < .001). Vertical stiffness, contact time, force at zero velocity, and propulsive duration increased (P < .05). According to statistical parametric mapping, braking (17%-25% of the movement) and propulsive forces (58%-81%) declined (P < .05). During the repeated bout, peak propulsive force and duration increased (P < .05), while mean propulsive force (P < .05) and GRF from 59% to 73% declined (P < .001). A repeated bout of DJs differed in propulsive GRF, without changes to the eccentric phase, or effects from CG.

Simple within-stride changes in treadmill speed can drive selective changes in human gait symmetry.

Millions of people walk with asymmetric gait patterns, highlighting a need for customizable rehabilitation approaches that can flexibly target different aspects of gait asymmetry. Here, we studied how simple within-stride changes in treadmill speed could drive selective changes in gait symmetry. In Experiment 1, healthy adults (n = 10) walked on an instrumented treadmill with and without a closed-loop controller engaged. This controller changed the treadmill speed to 1.50 or 0.75 m/s depending on whether the right or left leg generated propulsive ground reaction forces, respectively. Participants walked asymmetrically when the controller was engaged: the leg that accelerated during propulsion (right) showed smaller leading limb angles, larger trailing limb angles, and smaller propulsive forces than the leg that decelerated (left). In Experiment 2, healthy adults (n = 10) walked on the treadmill with and without an open-loop controller engaged. This controller changed the treadmill speed to 1.50 or 0.75 m/s at a prescribed time interval while a metronome guided participants to step at different time points relative to the speed change. Different patterns of gait asymmetry emerged depending on the timing of the speed change: step times, leading limb angles, and peak propulsion were asymmetric when the speed changed early in stance while step lengths, step times, and propulsion impulses were asymmetric when the speed changed later in stance. In sum, we show that simple manipulations of treadmill speed can drive selective changes in gait symmetry. Future work will explore the potential for this technique to restore gait symmetry in clinical populations.

Anticipatory effects on side-step cutting biomechanics in Women’s Australian Football League players

ObjectivesReactive side-step cutting manoeuvres are linked to anterior cruciate ligament (ACL) injuries in Women’s Australian Football League (AFLW) matches. We explored knee joint moments and ground reaction forces (GRFs) in...

“Posture first”: Interaction between posture and locomotion in people with low back pain during unexpectedly cued modification of gait initiation motor command

The ability to adapt anticipatory postural adjustments (APAs) in response to perturbations during single-joint movements is altered in people with chronic low back pain (LBP), but a comprehensive analysis during functional motor tasks is still missing. This study aimed to compare APAs and stepping characteristics during gait initiation between people with LBP and healthy controls, both in normal (without cue occurrence) condition and when an unexpected visual cue required to switch the stepping limb. Fourteen individuals with LPB and 10 healthy controls performed gait initiation in normal and switch conditions. The postural responses were evaluated through the analysis of center of pressure, propulsive ground reaction forces, trunk and whole-body kinematics, and activation onsets of leg and back muscles. During normal gait initiation, participants with LBP exhibited similar APAs and stepping characteristics to healthy controls. In the switch condition, individuals with LBP were characterized by greater mediolateral postural stability but decreased forward body motion and propulsion before stepping. The thorax motion was associated with forward propulsion parameters in both task conditions in people with LBP but not healthy controls. No between-group differences were found in muscle activation onsets. The results suggest that postural stability is prioritized over forward locomotion in individuals with LBP. Furthermore, the condition-invariant coupling between thorax and whole-body forward propulsion in LBP suggests an adaptation in the functional use of the thorax within the postural strategy, even in poor balance conditions.

Patients with unilateral ankle arthritis have decreased discrete and time-series limb symmetry compared to healthy controls.

Patients with ankle arthritis (AA) have side-to-side limb differences at the ankle and in spatiotemporal measures; however, the degree of symmetry between limbs has not been compared to a healthy population. The purpose of this study was to determine differences in limb symmetry during walking for discrete and time-series measures when comparing patients with unilateral AA to healthy participants. Thirty-seven AA and 37healthy participants were age, gender, and body mass indexmatched. Three-dimensional gait mechanics and ground reaction force(GRF) were captured during four to seven walking trails. GRFand hip and ankle mechanics were extracted bilaterally for each trial. The Normalized Symmetry Index and Statistical Parameter Mapping were used to assess discrete and time-series symmetry, respectively. Discrete symmetry was analyzed using linear mixed-effect models to determine significant differences between groups (α = 0.05). Compared to healthy participants, patients with AA had decreased weight acceptance (p = 0.017) and propulsive (p < 0.001) GRF, ankle plantarflexion (p = 0.021), ankle dorsiflexion (p = 0.010), and ankle plantarflexion moment (p < 0.001) symmetry. Significant regions of difference were found between limbs and groups throughout the stance phase for the vertical GRF force (p < 0.001), the ankle angle during push-off (p = 0.047), the plantarflexion moment (p < 0.001), and the hip extension angle (p = 0.034) and moment (p = 0.010). Patients with AA have decreased symmetry in the vertical GRF and at the ankle and hip during the weight acceptance and propulsive portions of the stance phase. Therefore, clinicians should try a non improving symmetry focusing on changing hip and ankle mechanics during the weight acceptance and propulsive phases of gait.

Effects of walking speed on magnitude and symmetry of ground reaction forces in individuals with transfemoral prosthesis

Individuals with unilateral transfemoral amputation (uTFA) walk asymmetrically. Investigating gait symmetry in ground reaction force (GRF) is critical because asymmetric loading on the residual limb can result in injury. The aim of this study was to investigate the GRF of individuals with uTFA by systematically controlling their walking at eight speeds(2.0–5.5 km/h with increments of 0.5 km/h) on a treadmill. Forty-eight individuals participated in this study, which included 24 individuals with uTFA (K3 and K4) and 24 individuals without amputation. GRFs (anteroposterior, mediolateral, and vertical) of the prosthetic and intact limb steps were collected for the individuals with uTFA and those of the right limb were collected for the control group. Peak force values of the GRF components, temporal parameters, impulses, and their asymmetry ratios were investigated and statistically analyzed. With an increasing walking speed, the magnitude of GRF changed gradually; individuals with uTFA exhibited increased GRF asymmetry in the vertical and mediolateral components, while that of the anteroposterior component remained constant. uTFA individuals typically maintained a constant asymmetry ratio in the mediolateral and anteroposterior (braking and propulsive) GRF impulses across a wide range of walking speeds. This result suggests that individuals with uTFA may cope with various walking speeds by maintaining symmetric mediolateral and anteroposterior impulses. The data provided in this study can serve as normative data for the GRF and its symmetry across a range of walking speeds in individuals with uTFA.

A comparison of centre of pressure behaviour and ground reaction force magnitudes when individuals walk overground and on an instrumented treadmill

BackgroundInstrumented treadmills facilitate analysis of consecutive strides in ways that typical overground gait data collections cannot. Researchers have quantified differences between joint kinetic measures whilst walking on an instrumented treadmill compared to those walking overground. The reason for such differences has not yet been established. Research QuestionCan we identify the source or sources of these errors by comparing centre of pressure and ground reaction force measurements recorded on a treadmill to those collected overground? MethodsKinematic and kinetic data were recorded while nineteen individuals walked continuously at their self-selected walking speed overground and on a treadmill. Comparisons of the centre of pressure and ground reaction forces were made between the two conditions using 2-tailed paired t-tests and Cohen’s d effect size. ResultsThe results indicated that participants had significantly faster backwards, lateral and medial centre of pressure velocities when walking on a treadmill compared to when they were walking overground. Additionally, participants also had significantly reduced peak propulsive ground reaction forces when walking on a treadmill than walking overground. SignificanceThese results suggest that shear forces caused by the belts sliding over the treadmill force platforms affect the centre of pressure during early stance, and the minimal acceleration of a participant’s centre of mass during treadmill walking results in reduced propulsive force during late stance. Therefore, care should be taken during studies when comparing kinetic gait variables between overground and treadmill walking.

Design of active ankle foot orthotics for gait assistance and fall prevention

An active ankle-foot orthosis (AAFO) was developed with the intent of providing propulsive ground reaction force to individuals at risk of experiencing fall. The device makes use of one double-acting cylinder per leg, and a lever arm system to transfer propulsive force to the ground, and potentially assist in fall prevention and rehabilitation. Preliminary tests have been shown to improve ground reaction forces in walking. In this paper, the design and construction of the device is included as well as the control algorithm used and testing procedure. This research may be used to advance the field of gait assistance and fall prevention through use of active foot orthotics.

Effects of Horizontal Impeding Force Gait Training on Older Adult Push-Off Intensity.

Aging and many gait pathologies are often characterized by deficits in push-off intensity (i.e., propulsive ground reaction forces and peak ankle moment and power output) during walking. Unfortunately, conventional interventions such as progressive resistance training, designed to enhance calf muscle mechanical output, generally fail to translate strength gains to functional improvements in habitual push-off intensity. Horizontal impeding forces applied to the body's center of mass systematically augment the mechanical output required from muscle-tendon units spanning the ankle during the push-off phase of walking, which could convey long-term benefits via training. Therefore, the purpose of this study was to investigate the preliminary efficacy of a 6-wk horizontal impeding force training paradigm on improving habitual push-off intensity in 11 healthy but not physically active older adults (age = 76 ± 4 yr, 6 females and 5 males). We found that older adults significantly (P < 0.05) increased measures of isometric strength by 18%, maximum walking speed by 10%, and 6-min walk test distance by 9% as a result of horizontal impeding force training. As a more clinically significant contribution of this work, we found that those subjects also increased habitual peak ankle moment and peak ankle power during push off after training by a significant 10% and 15%, respectively (P ≤ 0.036). We conclude that the use of horizontal impeding forces in older adults improves their maximum muscular and walking capacities while encouraging access to newfound strength gains, thereby improving habitual push-off intensity during walking.

Effect Of Footwear On Leg Stiffness Of Female Athletes

Leg stiffness is a fundamental property of the lower limb spring pattern, and is expressed by the ratio of the maximum vertical ground reaction force (GRF) to the vertical displacement of the body’s center of mass. The foot-ground interface, i.e. the footwear (FW), is an important factor that contributes to the functional leg stiffness. PURPOSE:. To examine the FW effect on leg stiffness of young female athletes in a variety of team sports. METHODS: Twenty - six female basketball, handball and volleyball players (24.9 ± 6.1 years, height 176.4 ± 7.6 cm, body mass 71.0 ± 6.9 kg) performed 30 s of two-legged hopping in place, barefoot (BF) and with their usual FW, at a preset hopping frequency (digital metronome at 2.2 Hz which approximates the natural hopping frequency). Two-legged hopping was performed on a force platform (Κistler 9260AA, 1000Hz, Bioware Software 2812 A1-3) which was used to record the vertical GRF. The variables used for the statistical analysis of the FW effect were extracted from 10 consecutive hops, and were analyzed using two-way ANOVA (p<0.05). RESULTS: leg stiffness was significantly increased in the FW condition, both in absolute (BF: 32.7 ± 8.5 kN/m, FW: 36.9±8.3 kN/m, p = 0.014), as well as in relative to body mass values (BF: 0.478 ± 0.101 kN/m/kg, FW: 0.520 ± 0.110 kN/m/kg (p = 0.017). Also, despite the instruction to follow the same hopping frequency as set by the digital metronome in both the BF and the FW, hopping duration was shortened (BF: 0.469 ± 0.022 s, FW: 0.430 ± 0.013 s, p = 0.001) and the propulsive vertical GRF was increased (BF: 32.4 ± 4.7 N/kg, FW: 33.7 ± 5.6 N/kg, p = 0.048) in the FW condition. CONCLUSIONS: FW appears to increase leg stiffness, which may favor the myotendinous force transfer and contribute to a more effective lower limb spring pattern.

The Characterization Of The Transition Phase During A 180° Change Of Direction Task

The evaluation of change of direction ability should not merely rely on the measurement of total sprinting time, but it should focus also on the understanding of specific movement patterns. PURPOSE: To evaluate the transition phase (TP) during a 180° change of direction (COD) task. METHODS: 14 recreational basketball athletes (age: 21.4±2.6 years) were evaluated during a 10-m COD test. TP has been identified considering 3 consecutive steps (i.e., final decelerating foot contact [DFC], turning foot contact [TFC], first accelerating foot contact [AFC]), using two force platforms. Differences in total (TCT), braking (BCT), and propulsive (PCT) contact time, vertical braking (VBGRF) and propulsive (VPGRF) ground reaction force (relative to body mass), and vertical braking (VBI), propulsive (VPI), and total (VTI) impulse (relative to body mass) were evaluated in relation to leg preference, the 3 steps, and groups (slower vs. faster defined as those below and above the 50th percentile of total sprinting time). RESULTS: No differences emerged for leg preference. TP (1.199±0.11 s) contributed for an average of 42.6±3.4% to the total sprinting time (2.817±0.14 s), with DFC involving only a braking action, whilst TFC and AFC comprising both a braking and propulsive action. Differences (p<0.05) among the 3 steps emerged for TCT (DFC: 0.380±0.07 s; TFC: 0.525±0.06 s; and AFC: 0.303±0.04 s), VBGRF (DFC: 22.7±7.5 N·kg-1; TFC: 20.3±2.8 N·kg-1; and AFC: 8.1±2.7 N·kg-1), VBI (DFC: 2.1±0.4 m·s-1; TFC: 2.5±0.5 m·s-1; and AFC: 0.4±0.2 m·s-1), and VTI (DFC: 2.1±0.4 m·s-1; TFC: 5.6±0.6 m·s-1; and AFC: 2.6±0.3 m·s-1). Furthermore, differences (p<0.05) between TCF and AFC were evident for VPGRF (TFC: 14±1.2 N·kg-1; and AFC: 15.6±1.7 N·kg-1) and VPI (TFC: 3.1±0.6 m·s-1; and AFC: 2.2±0.4 m·s-1). Differences between groups emerged in the TFC only, with faster individuals demonstrating shorter TCT (0.489±0.1 s) and PCT (0.281±0.1 s), and lower VPI (2.8±0.5 m·s-1) compared to slower individuals (TCT: 0.542±0.1 s; PT: 0.339±0.1 s; and VPI 3.4±0.6 m·s-1). CONCLUSIONS: Findings revealed specific movement patterns during the TP of a COD task and the central role played by the turning step in differentiating faster and slower recreational basketball athletes, with potential further implications for future testing and training procedures.

Peak horizontal ground reaction forces and impulse correlate with segmental energy flow in youth baseball pitchers

The purpose of this study was to determine associations between horizontal ground reaction force (GRF) kinetics and energy flow (EF) variables in youth baseball players. Twenty-four youth baseball players pitched fastballs in an indoor laboratory while motion capture and force plate data were collected. Horizontal GRF variables were extracted (peak GRF and GRF impulse) while EF was calculated by integrating magnitudes of mechanical powers transferred into and out of the pelvis, trunk, and arm segments via joint force power (JFP) and joint moment power (JMP) components. Peak propulsive GRF of the drive (back) leg correlated with EF into proximal segments, whereas peak braking GRF of the stride (lead) leg correlated with EF into distal segments. Furthermore, peak GRF of the drive leg and GRF impulse of both legs correlated with the JFP components of EF into the pelvis and trunk segments. In contrast, peak GRF and GRF impulse of the stride leg both correlated with the JMP components of EF into the arm segment. These results suggest that horizontal GRF impulse from the drive and stride leg contribute to EF between major segments of the lower and upper extremity. In addition, these results also suggest that propulsion kinetics of the drive leg play a role in transferring linear power via the pelvis and trunk segments in the throwing direction of the pitch, whereas braking kinetics of the stride leg play a role in creating rotational power that is transferred between the trunk and arm segment via the shoulder joint.

Acute kinematics and kinetics changes to wearable resistance during change of direction among soccer players

ABSTRACT This study determined the acute changes in kinematics and kinetics when an additional load equivalent to 5% body mass was attached to the torso during change of direction (COD). In this within-subject repeated measures study, 14 male soccer players (age: 18.29 ± 0.32 years) volunteered to participate. Subjects performed COD under two conditions in randomized order: (1) no WR, and (2) with WR. No significant differences between the loaded and unloaded conditions in actual COD angle, approach speed, braking time, propulsive time, contact time, COD completion time (all p > 0.05, ES = 0.05–0.11), and all measured kinematic parameters (all p > 0.05, ES = 0–0.18). Nonetheless, ankle plantar/dorsi flexion ROM had possibly small increase in the loaded condition (ES = 0.24). Kinetics analysis has shown that the loaded condition was likely to have small increase in relative peak vertical propulsive ground reaction force (GRF, p = 0.11, ES = 0.41), and possible small increases in relative peak braking GRF (vertical: p = 0.21, ES = 0.42; total: p = 0.22, ES = 0.38), relative peak total propulsive GRF (p = 0.24, ES = 0.26), and relative braking impulse (horizontal, vertical, and total; p = 0.27–0.41, ES = 0.26–0.28). WR did not significantly change the acute movement techniques, meanwhile induced small increases in important kinetic stimuli for potential adaptation in COD.

What goes up must come down: Consequences of jump strategy modification on dance leap take-off biomechanics

ABSTRACT Chronic foot and ankle injuries are common in dancers; understanding how lower extremity loading changes in response to altered task goals can be beneficial for rehabilitation and injury prevention strategies. The purpose of this study was to examine mechanical demands during jump take-offs when the task goal was modified to focus on either increasing jump distance or increasing jump height. It was hypothesized that a jump strategy focused on height would result in decreased energetic demands on the foot and ankle joints. Thirty healthy, experienced female dancers performed saut de chat leaps while travelling as far as possible (FAR) or jumping as high as possible (UP). Ground reaction force (GRF) impulses and peak sagittal plane net joint moments and sagittal plane mechanical energy expenditure (MEE) of the metatarsophalangeal (MTP), ankle, knee, and hip joints were calculated. During take-off, vertical and horizontal braking GRF impulses were greater and horizontal propulsive GRF impulse was lower in the UP condition. MEE at the MTP, ankle, and hip joints was lower in UP, and MEE at the knee was higher in UP. These results suggest that a strategy focused on height may be helpful in unloading the ankle and MTP joints during dance leaps.

Increasing the Propulsive Demands of Walking to their Maximum Elucidates Functionally Limiting Impairments in Older Adult Gait.

We elucidated functional limitations in older adult gait by increasing horizontal impeding forces and walking speed to their maximums compared to dynamometry and to data from their young counterparts. Specifically, we investigated which determinants of push-off intensity represent genuine functionally limiting impairments in older adult gait versus biomechanical changes that do not directly limit walking performance. We found that older adults walked at their preferred speed with hallmark deficits in push-off intensity. These subjects were fully capable of overcoming deficits in propulsive ground reaction force, trailing limb positive work, trailing leg and hip extension, and ankle power generation when the propulsive demands of walking were increased to maximum. Of the outcomes tested, age-related deficits in ankle moment emerged as the lone genuine functionally limiting impairment in older adults. Distinguishing genuine functional limitations from age-related differences masquerading as limitations represents a critical step toward the development and prescription of effective interventions.

The relationship between neck angles and ground reaction forces in schoolchildren during backpack carriage

Summary Study aim: This study aimed to examine the effect of carrying backpacks on neck posture and ground reaction forces (GRFs) and to investigate the relationship between neck angles and GRFs during backpack carriage in schoolchildren. Material and methods: The craniohorizontal angle (CHA), craniovertebral angle (CVA), sagittal shoulder posture (SSP) and GRFs were measured in right-handed schoolchildren (14 male and 12 female) with mean age 10.17 ± 1.15 years during loaded and unloading conditions. The Qualisys motion analysis system with a force plate was used to assess the neck angles and GRFs. Results: During backpack carriage there was a significant increase in the CHA (p = 0.001), significant decrease in the CVA and SSP (p = 0.001, 0.016 respectively), no significant difference in the normalized (scaled to body weight) vertical GRFs (p &gt; 0.05), and a significant increase in the anterior braking and posterior propulsive GRFs (p = 0.035, 0.002 respectively) compared to the unloading condition. While carrying a backpack there was a moderate negative correlation between the SSP and first vertical GRF (r = –0.464) and a strong negative correlation with the second vertical GRF (r = –0.571) and the posterior propulsive GRF (r = –0.587). Conclusion: Carrying a backpack weighing 15% of the child’s body weight changes the head posture and increases the normalized value of the anterior-posterior shear force. During backpack carriage, decreasing the SSP is associated with increasing the load acceptance, thrusting and posterior propulsive forces. Increasing the shearing force may lead to development of postural abnormities. Consequently, the ideal backpack weight should be considered by parents and teachers.

The stiff plate location into the shoe influences the running biomechanics

ABSTRACT The changes in running biomechanics induced by an increased longitudinal bending stiffness (stiff plates added into the shoes) have been well investigated, but little is known concerning the effects of the stiff plate location into the shoe on running biomechanics. Fourteen male recreational runners ran at two participant-specific running speeds (3.28 ± 0.28 m/s and 4.01 ± 0.27 m/s) with two shoe conditions where a stiff plate was added either in high (under the insole) or low location (between the midsole and outsole). Ground reaction forces, lower limb joint angles, net joint torques and work, as well as alignment between the resultant ground reaction force and the leg were analysed. Among the running speeds performed by the runners, the high location significantly decreased propulsive ground reaction forces, increased metatarsophalangeal joint dorsiflexion and ankle plantarflexion, induced an increased alignment between the resultant ground reaction force and the runner’s leg, thus decreasing all the lower limb joint torques and the positive work at the knee joint compared to the low location. The results suggested that the high stiff plate location into the shoe should be considered for running performance perspectives, but care should be taken to not alter the perceived comfort and/or increase injury risks.

Ankle power biofeedback attenuates the distal-to-proximal redistribution in older adults

BackgroundCompared to young adults, older adults walk slower, with shorter strides, and with a characteristic decrease in ankle power output. Seemingly in response, older adults rely more than young on hip power output, a phenomenon known as a distal-to-proximal redistribution. Nevertheless, older adults can increase ankle power to walk faster or uphill, revealing a translationally important gap in our understanding. Research questionOur purpose was to implement a novel ankle power biofeedback paradigm to encourage favorable biomechanical adaptations (i.e. reverse the distal-redistribution) during habitual speed walking in older adults. Methods10 healthy older adults walked at their preferred speeds while real-time visual biofeedback provided target increases and decreases of 10 and 20% different from preferred ankle power. We evaluated the effect of changes in ankle power on joint kinetics, kinematics, and propulsive ground reaction forces. Pre and post overground walking speed assessments evaluated the effect of increased ankle power recall on walking speed. ResultsBiofeedback systematically elicited changes in ankle power; increasing and decreasing ankle power by 14% and 17% when targeting ±20% different from preferred, respectively. We observed a significant negative correlation between ankle power and hip extensor work. Older adults relied more heavily on changes in ankle angular velocity than ankle moment to modulate ankle power. Lastly, older adults walked almost 11% faster when recalling increased ankle power overground. SignificanceOlder adults are capable of increasing ankle power through targeted ankle power biofeedback – effects that are accompanied by diminished hip power output and attenuation of the distal-to-proximal redistribution. The associated increase in preferred walking speed during recall suggests a functional benefit to increased ankle power output via transfer to overground walking. Further, our mechanistic insights allude to translational success using ankle angular velocity as a surrogate to modulate ankle power through biofeedback.

Evaluation of spring-loaded cane ground reaction forces during walking using time and frequency domain analysis

This study examined the effect of a spring-loaded cane stiffness reduction on upper and lower extremity ground reaction forces in time and frequency domain during cane-aided walking. Twenty-nine participants walked five times over two force plates with a spring-loaded cane set at four different stiffnesses and T-scope knee brace set at 30° of knee flexion to simulate a foot injury. Time–frequency domain analyses revealed an increase in ground reaction forces at the simulated injured foot and a decrease in ground reaction forces at the hand via the shaft of the cane for each spring loaded-cane stiffness reduction during walking. The results build on existing literature and highlight the use of spring-loaded canes, braking and propulsive ground reaction force measures, and frequency domain analysis to more accurately assess and monitor the rehabilitation and prevention of upper and lower extremity injuries during cane-aided walking.

The effects of downhill slope on kinematics and kinetics of the lower extremity joints during running

BackgroundThe purpose of this study was to investigate how lower extremity kinematics and kinetics change when running downhill. MethodsFifteen male recreational runners ran on an instrumented treadmill with three different slope conditions [level (0°), moderate (−6°), and steep (−9°)] at a controlled speed of 3.2 m/s. Ten consecutive steps were selected for analysis for each of the slope conditions and the order of slope conditions was randomized. Synchonized motion analysis and force plate were used to determine joint kinematics and kinetics. ResultsCompared to level running, participants demonstrated significantly larger knee flexion but smaller ankle plantar-flexion and hip flexion during downhill running (Ps < 0.05). Significantly smaller peak propulsive ground reaction forces and posterior impulses were found during downhill running (Ps < 0.05). Furthermore, participants experienced significantly larger extension moment and negative joint power at the knee (Ps < 0.05) but smaller plantar-flexion moment and negative joint power at the ankle during downhill running (Ps < 0.05). Negative net joint work increased for all joints with increased declinations and the knee joint showed the greatest increase in negative net joint work amongst the three joints (Ps < 0.05). SignificanceThese findings indicate that runners modify their running mechanics resulting in greater kinetic demand on the knee during downhill running. Differences in lower extremity injury mechanisms with different running slopes may be linked to the changes in loading at the knee but further investigation using clinical trials is needed to support the potential relationship.