Peak Propulsive Force Research Articles

We Will, We Will Shock You: Adaptive Versus Conventional Functional Electrical Stimulation in Individuals Post-Stroke.

Functional electrical stimulation (FES) is often used in poststroke gait rehabilitation to address decreased walking speed, foot drop, and decreased forward propulsion. However, not all individuals experience clinically meaningful improvements in gait function with stimulation. Previous research has developed adaptive functional electrical stimulation (AFES) systems that adjust stimulation timing and amplitude at every stride to deliver optimal stimulation. The purpose of this work was to determine the effects of a novel AFES system on functional gait outcomes and compare them to the effects of the existing FES system. Twenty-four individuals with chronic poststroke hemiparesis completed 64-min walking trials on an adaptive and fixed-speed treadmill with no stimulation, stimulation from the existing FES system, and stimulation from the AFES system. There was no significant effect of stimulation condition on walking speed, peak dorsiflexion angle, or peak propulsive force. Walking speed was significantly faster and peak propulsive force was significantly larger on the adaptive treadmill (ATM) than the fixed-speed treadmill (both p < 0.0001). Dorsiflexor stimulation timing was similar between stimulation conditions, but plantarflexor stimulation timing was significantly improved with the AFES system compared to the FES system (p = 0.0059). Variability between and within subjects was substantial, and some subjects experienced clinically meaningful improvements in walking speed, peak dorsiflexion angle, and peak propulsive force. However, not all subjects experienced benefits, suggesting that further research to characterize which subjects exhibit the best instantaneous response to FES is needed to optimize poststroke gait rehabilitation using FES.

The dynamic strength index is a reliable and feasible tool to assess neuromuscular performance in male and female handball players

ABSTRACT The aim of this study was to explore the reliability and feasibility of the isometric mid-thigh pull (IMTP) and dynamic strength index (DSI) in semi-professional handball players (seventeen male and eighteen female). A cross-sectional design was used to determine the test-retest reliability of several kinetic metrics registered with a force plates. The peak force, peak relative force, rate of force development (RFD 0–250 ms), and impulse 0–250 ms were selected from the IMTP test, whereas the peak propulsive force was chosen from the countermovement jump test to obtain the DSI. The intraclass correlation coefficient (ICC), coefficient of variation (CV), standard error of the measurement (SEM) and smallest detectable difference (SDD) were calculated. A paired sample t-test was also performed. No significant differences were found between the testing sessions for all variables, except for peak propulsive force for all players (p = 0.036) and DSI for female players (p = 0.037). Reliability for all kinetic metrics was good to excellent (ICC = 0.78–0.97), with low variability (CV ≤ 8.64%), being the SEM scores lower than SDD. In conclusion, the IMTP test and DSI are highly reliable and feasible tools for assessing neuromuscular performance in semi-professional handball players.

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.

Adaptive Functional Electrical Stimulation Delivers Stimulation Amplitudes Based on Real-Time Gait Biomechanics.

Functional electrical stimulation (FES) is often used in poststroke gait rehabilitation to decrease foot drop and increase forward propulsion. However, not all stroke survivors experience clinically meaningful improvements in gait function following training with FES. The purpose of this work was to develop and validate a novel adaptive FES (AFES) system to improve dorsiflexor (DF) and plantarflexor (PF) stimulation timing and iteratively adjust the stimulation amplitude at each stride based on measured gait biomechanics. Stimulation timing was determined by a series of bilateral footswitches. Stimulation amplitude was calculated based on measured dorsiflexion angle and peak propulsive force, where increased foot drop and decreased paretic propulsion resulted in increased stimulation amplitudes. Ten individuals with chronic poststroke hemiparesis walked on an adaptive treadmill with adaptive FES for three 2-min trials. Stimulation was delivered at the correct time to the dorsiflexor muscles during 95% of strides while stimulation was delivered to the plantarflexor muscles at the correct time during 84% of strides. Stimulation amplitudes were correctly calculated and delivered for all except two strides out of nearly 3000. The adaptive FES system responds to real-time gait biomechanics as intended, and further individualization to subject-specific impairments and rehabilitation goals may lead to improved rehabilitation outcomes.

Visual feedback improves propulsive force generation during treadmill walking in people with Parkinson disease

Persons with Parkinson's disease experience gait alterations, such as reduced step length. Gait dysfunction is a significant research priority as the current treatments targeting gait impairment are limited. This study aimed to investigate the effects of visual biofeedback on propulsive force during treadmill walking in persons with Parkinson's. Sixteen ambulatory persons with Parkinson's participated in the study. They received real-time biofeedback of anterior ground reaction force during treadmill walking at a constant speed. Peak propulsive force values were measured and normalized to body weight. Spatiotemporal parameters were also assessed, including stride length and double support percent. Persons with Parkinson's significantly increased peak propulsive force during biofeedback compared to baseline (p <.0001, Cohen's dz = 1.69). Variability in peak anterior ground reaction force decreased across repeated trials (p <.0001, dz = 1.51). While spatiotemporal parameters did not show significant changes individually, stride length and double support percent improved marginally during biofeedback trials. Persons with Parkinson's can increase propulsive force with visual biofeedback, suggesting the presence of a propulsive reserve. Though stride length did not significantly change, clinically meaningful improvements were observed. Targeting push-off force through visual biofeedback may offer a potential rehabilitation technique to enhance gait performance in Persons with Parkinson's. Future studies could explore the long-term efficacy of this intervention and investigate additional strategies to improve gait in Parkinson's disease.

Comparative kinetics of humans and non-human primates during vertical climbing.

Climbing represents a critical behavior in the context of primate evolution. However, anatomically modern human populations are considered ill-suited for climbing. This adaptation can be attributed to the evolution of striding bipedalism, redirecting anatomical traits away from efficient climbing. Although prior studies have speculated on the kinetic consequences of this anatomical reorganization, there is a lack of data on the force profiles of human climbers. This study utilized high-speed videography and force plate analysis to assess single limb forces during climbing from 44 human participants of varying climbing experience and compared these data with climbing data from eight species of non-human primates (anthropoids and strepsirrhines). Contrary to expectations, experience level had no significant effect on the magnitude of single limb forces in humans. Experienced climbers did, however, demonstrate a predictable relationship between center of mass position and peak normal forces, suggesting a better ability to modulate forces during climbing. Humans exhibited significantly higher peak propulsive forces in the hindlimb compared with the forelimb and greater hindlimb dominance overall compared with non-human primates. All species sampled demonstrated exclusively tensile forelimbs and predominantly compressive hindlimbs. Strepsirrhines exhibited a pull-push transition in normal forces, while anthropoid primates, including humans, did not. Climbing force profiles are remarkably stereotyped across humans, reflecting the universal mechanical demands of this form of locomotion. Extreme functional differentiation between forelimbs and hindlimbs in humans may help to explain the evolution of bipedalism in ancestrally climbing hominoids.

Propulsive forces and muscle activation during gait: comparisons between premenopausal and postmenopausal midlife women.

The aim of this study was to investigate whether there is a reduction in propulsive force during gait in postmenopausal women compared with premenopausal women. Forty-four women (21 premenopausal and 23 postmenopausal women) aged 40 to 55 years were selected. The ability to reach peak propulsive forces was assessed during the step execution test. The test was performed at the usual speed on 2 nonconsecutive days, with two attempts per day, using a force platform. Four temporal parameters were defined and calculated: initiation phase, preparation phase, swing phase, and total time. Peak force (anteroposterior and vertical) and time to reach peak force were obtained in both preparation and swing phases. The rate of force development was defined as peak force divided by time to reach peak force. The postmenopausal women group presented a longer time in the preparation phase (540.6 ± 77 ms vs 482.5 ± 93 ms, P = 0.024) and consequently a longer total time in the step execution test (1,191 ± 106.4 ms vs 1,129 ± 114.3 ms, P = 0.045). There were differences between the groups for the rate of force development in the anteroposterior (postmenopausal women, 142.5 ± 38.1 N/s vs premenopausal women, 174.7 ± 70.5 N/s; P = 0.022) and vertical directions in the preparation phase (postmenopausal women, 102.7 ± 62.3 N/s vs premenopausal women, 145.3 ± 71 N/s; P = 0.012). No significant differences ( P > 0.05) were found in force, time to peak force, and rate of force development during the swing phase. In addition, there were no observed differences in surface electromyography of the medial and lateral gastrocnemius muscles during the preparation phase and swing phase of the step execution test between the two groups. Postmenopausal women exhibited lower ability to generate propulsive force rapidly (rates of force development) in both the anteroposterior and vertical directions during the preparation phase of gait compared with premenopausal women. This indicates that postmenopausal women experience a reduction in propulsive force during gait.

Synergistic Dominance Induced by Hip Extension Exercise Alters Biomechanics and Muscular Activity During Sprinting and Suggests a Potential Link to Hamstring Strain.

Iguchi, J, Hojo, T, Fujisawa, Y, Kuzuhara, K, Yanase, K, Hirono, T, Koyama, Y, Tateuchi, H, and Ichihashi, N. Synergistic dominance induced by hip extension exercise alters biomechanics and muscular activity during sprinting and suggests a potential link to hamstring strain. J Strength Cond Res 37(9): 1770-1776, 2023-Hamstring strain is likely to occur during the late swing phase or the first half of the stance phase in sprinting. During the late swing phase, the hamstrings and gluteus maximus (Gmax) contract eccentrically to decelerate the lower limb. We hypothesized that, when the Gmax becomes dysfunctional because of delayed onset muscle soreness (DOMS), the hamstring workload is increased (i.e., there is synergetic dominance), which could lead to an increased risk of strain. A total of healthy 15 male undergraduate or graduate students (age 23.1 ± 1.28 years) were recruited to perform exercises and maximal sprints. On day 1, before subjects performing DOMS-causing exercises, and on day 3, while subjects were experiencing DOMS in the Gmax, lower-limb biomechanical and muscle activity data were recorded using a motion analysis system and electromyography (EMG), respectively. Data were analyzed and compared between day 1 and day 3. Hip flexion angle on day 3 was significantly lower than that on day 1, but the opposite was true for the knee flexion angle (P < 0.05). Vastus medialis (VM), biceps femoris (BF), and Gmax muscle activities on day 3 were significantly higher than those on day 1 (P < 0.05). Peak propulsive forces on day 3 were significantly higher than those on day 1 (P < 0.05). Kinematic changes such as decreased hip flexion angle and EMG changes such as increased BF EMG activity on day 3 to compensate for the loss of function of the Gmax may potentially increase the risk of hamstring strain.

Acclimatization of force production during walking in persons with Parkinson's disease

Individuals with Parkinson’s disease walk slowly, with short strides resulting in decreased mobility. Treadmill walking assessments are utilized to understand gait impairment in persons with Parkinson’s disease and treadmill-based interventions to mobility have become increasingly popular. While walking on a treadmill, there is a reported initial acclimatization period where individuals adjust to the speed and dynamics of the moving belt before producing consistent walking patterns. It is unknown how much walking time is required for individuals with Parkinson’s disease to acclimate to the treadmill. We investigated how spatiotemporal parameters and ground reaction forces changed during treadmill acclimatization. Twenty individuals with idiopathic Parkinson’s (15 Males, 5 Females) walked for a five-minute treadmill session on an instrumented treadmill while motion capture data were collected. The measures of interest included ground reaction force measures (peak propulsive force, peak braking force, propulsive impulse, and braking impulse) and spatiotemporal measures (stride length, stride time, or double support time). Analyses demonstrated significantly increased propulsive impulse (p <.001) after the first minute, with no significant difference for the remaining minutes (p ≥ 0.395). There were no significant changes in the spatiotemporal measures (P =.065). These results quantify the stabilization of ground reaction force during the treadmill acclimatization period. Based on our findings, if steady-state gait is desired, we recommend participants walk for at least two minutes before data collection. Future clinical investigations should consider ground reaction force as sensitive parameters for evaluating gait in persons with Parkinson’s disease in treadmill-based assessments or interventional therapies.

The Ecological Validity of Countermovement Jump to On-Court Asymmetry in Basketball.

Jump-based asymmetry is often used as an indicator of sport performance and may be used to discern injury susceptibility. Due to task specificity, however, countermovement jump asymmetry may not be representative of on-court asymmetry. As such, we assessed the association between countermovement jump asymmetry and on-court impact asymmetry metrics (n=3, and n=4, respectively) using linear regressions (α=0.05). Fifteen female basketball athletes completed countermovement jump and on-court sessions across a competitive season. A significant negative association was found between peak landing force asymmetry and both overall and medium acceleration on-court asymmetry (b=-0.1, R 2 =0.08, p<0.001; b=-0.1, R 2 =0.11, p<0.001, respectively), as well as between peak propulsive force asymmetry and on-court medium acceleration asymmetry (b=-0.24, R 2 =0.04, p=0.01). Alternatively, both peak landing and peak propulsive force asymmetry were significantly positively associated with on-court high acceleration asymmetry (b=0.17, R 2 =0.08, p<0.001; b=0.35, R 2 =0.02, p=0.04, respectively). While some overlap may exist, countermovement jump and on-court impact asymmetry appear to be independent. Thus, sport-specific monitoring may be necessary to adequately monitor injury susceptibility using asymmetry.

Positional Comparison of Jump Performance in NCAA Division I Female Volleyball Athletes

Background: The vertical jump task is a critical component of success in volleyball. Each position on the court has its own physical demands and has differing levels of vertical jump task demands. Objective: Thus, the objective of this investigation was to compare vertical jump performance between the two positional groups using the countermovement jump (CMJ) and squat jump (SJ). Methods: Using an observational cross-sectional study design, nineteen NCAA Division I female volleyball athletes participated in this investigation. Participants first performed three CMJ trials followed by 3 SJ trials on a force platform. Jump height, peak and mean net propulsive forces, and time to take off were calculated for both the CMJ and SJ. Reactive strength index modified and propulsive duration were additionally calculated for the CMJ and average RFD for the SJ. Independent sample t-tests were performed comparing positional groups on each variable of interest with Hedges g effect sizes additionally calculated. Results: No statistically significant differences (p 0.05) were found between any of the variables of interest in the CMJ though moderate effect sizes were seen in jump height (g =0.78). No statistically significant differences were present in the SJ though moderate effect sizes were seen in RFD (g = 0.65), mean propulsive force (g = 0.79) and peak propulsive force (g = 0.66). Discussion: As the vertical jump task is a critical task for high-level performance in both positions, and the no differences seen between groups, training programs should be designed to improve jump performance with special attention to the individual athletes’ needs rather than the specifics of the playing position.

Force plate analysis of ground reaction forces in relation to gait velocity of healthy Beagles

To evaluate changes in ground reaction forces (GRFs) in relation to gait velocity using 2 force plates (FPs) for healthy Beagles. 18 healthy Beagles were included (body weight, 10.45 ± 1.28 kg; age, 26 ± 11 months). Ten GRF parameters were measured at three gait velocities (walk, 0.9 to 1.2 m/s; trot 1, 1.6 to 2.0 m/s; and trot 2, 2.1 to 2.5 m/s): peak lateral force (PLF), peak medial force (PMF), lateral impulse (LI), medial impulse (MI), peak propulsive force (PPF), peak braking force (PBF), propulsive impulse (PI), braking impulse (BI), peak vertical force (PVF), and vertical impulse (VI). As velocity increased, the PVF of all limbs increased, the VI of all limbs decreased, and the PPF of the forelimbs increased. At all velocities, PBF and BI were significantly higher than the PPF and PI in forelimbs; however, PBF and BI were significantly lower than the PPF and PI in hindlimbs. There were no significant differences in the PLF, PMF, LI, and MI of the forelimbs and hindlimbs among all velocities. The PLF was significantly higher than the PMF of forelimbs during trot 1 and trot 2. These results may be useful when comparing healthy Beagles with diseased ones when premorbid data are not available. Because the forelimbs are mainly responsible for the braking force, it is suggested that weight bearing is more stable in the forelimbs than in the hindlimbs, which are mainly responsible for the propulsive force, and that a greater force is generated laterally than medially during trot.

The Impact of COVID-19 and Muscle Fatigue on Cardiorespiratory Fitness and Running Kinetics in Female Recreational Runners.

Background: There is evidence that fully recovered COVID-19 patients usually resume physical exercise, but do not perform at the same intensity level performed prior to infection. The aim of this study was to evaluate the impact of COVID-19 infection and recovery as well as muscle fatigue on cardiorespiratory fitness and running biomechanics in female recreational runners. Methods: Twenty-eight females were divided into a group of hospitalized and recovered COVID-19 patients (COV, n = 14, at least 14 days following recovery) and a group of healthy age-matched controls (CTR, n = 14). Ground reaction forces from stepping on a force plate while barefoot overground running at 3.3 m/s was measured before and after a fatiguing protocol. The fatigue protocol consisted of incrementally increasing running speed until reaching a score of 13 on the 6–20 Borg scale, followed by steady-state running until exhaustion. The effects of group and fatigue were assessed for steady-state running duration, steady-state running speed, ground contact time, vertical instantaneous loading rate and peak propulsion force. Results: COV runners completed only 56% of the running time achieved by the CTR (p < 0.0001), and at a 26% slower steady-state running speed (p < 0.0001). There were fatigue-related reductions in loading rate (p = 0.004) without group differences. Increased ground contact time (p = 0.002) and reduced peak propulsion force (p = 0.005) were found for COV when compared to CTR. Conclusion: Our results suggest that female runners who recovered from COVID-19 showed compromised running endurance and altered running kinetics in the form of longer stance periods and weaker propulsion forces. More research is needed in this area using larger sample sizes to confirm our study findings.

Adaptive treadmill walking encourages persistent propulsion

BackgroundAdaptive treadmills allow real-time changes in walking speed by responding to changes in step length, propulsion, or position on the treadmill. The stride-to-stride variability, or persistence, of stride time during overground, fixed-speed, and adaptive treadmill walking has been studied, but persistence of propulsion during adaptive treadmill walking remains unknown. Because increased propulsion is often a goal of post-stroke rehabilitation, knowledge of the stride-to-stride variability may aid rehabilitation protocol design. Research questionHow do spatiotemporal and propulsive gait variables vary from stride to stride during adaptive treadmill walking, and how do they compare to fixed-speed treadmill walking? MethodsEighteen young healthy subjects walked on an instrumented split-belt treadmill in the adaptive and fixed-speed modes for 10 minutes at their comfortable speed. Kinetic data was collected from the treadmill. Detrended fluctuation analysis was applied to the time series data. Shapiro-Wilk tests assessed normality and one-way repeated measures ANOVAs compared between adaptive, fixed-speed, and randomly shuffled conditions at a Bonferroni-corrected significance level of 0.0055. ResultsStride time, stride length, step length, and braking impulse were persistent (α > 0.5) in the adaptive and fixed-speed conditions. Adaptive and fixed-speed were different from each other. Stride speed was persistent in the adaptive condition and anti-persistent (α < 0.5) in the fixed-speed condition. Peak propulsive force, peak braking force, and propulsive impulse were persistent in the adaptive condition but not the fixed-speed condition (α ≈ 0.5). Net impulse was non-persistent in the adaptive and fixed-speed conditions. All variables were non-persistent in the shuffled condition. SignificanceDuring adaptive treadmill walking, increases in propulsive force and impulse persist for multiple strides. Persistence was stronger on the adaptive treadmill, where increased propulsion translates into increased walking speed. For post-stroke gait rehabilitation where increasing propulsion and speed are goals, the stronger persistence of adaptive treadmill walking may be beneficial.

Ground Reaction Force Differences between Bionic Shoes and Neutral Running Shoes in Recreational Male Runners before and after a 5 km Run.

Running-related injuries are common among runners. Recent studies in footwear have shown that designs of shoes can potentially affect sports performance and risk of injury. Bionic shoes combine the functions of barefoot running and foot protection and incorporate traditional unstable structures based on bionic science. The purpose of this study was to investigate ground reaction force (GRF) differences for a 5 km run and how bionic shoes affect GRFs. Sixteen male recreational runners volunteered to participate in this study and finished two 5 km running sessions (a neutral shoe session and a bionic shoe session). Two-way repeated-measures ANOVAs were performed to determine the differences in GRFs. In the analysis of the footwear conditions of runners, bionic shoes showed significant decreases in vertical impulse, peak propulsive force, propulsive impulse, and contact time, while the braking impulse and vertical instantaneous loading rate (VILR) increased significantly compared to the neutral shoes. Main effects for a 5 km run were also observed at vertical GRFs and anterior–posterior GRFs. The increases of peak vertical impact force, vertical average loading rate (VALR), VILR, peak braking force and braking impulse were observed in post-5 km running trials and a reduction in peak propulsive force and propulsive impulse. The interaction effects existed in VILR and contact time. The results suggest that bionic shoes may benefit runners with decreasing injury risk during running. The findings of the present study may help to understand the effects of footwear design during prolonged running, thereby providing valuable information for reducing the risk of running injuries.

Lower-limb Force And Fat-free Mass Asymmetries And Their Relationships To Vertical Jump Performance

The countermovement (CMJ) and squat jump (SJ) assess force and power production of the lower-limbs. The relationship of jumping force asymmetries to lower-limb fat-free mass (MM) asymmetries has not been well-studied. PURPOSE: The purpose of this study was to examine the relationship between CMJ and SJ performance and lower-limb MM asymmetries. METHODS: 38 Division II male lacrosse athletes performed the CMJ and SJ on bilateral force plates and their body composition was assessed via segmental bioelectrical impedance analysis. Relationships between peak and left-to-right landing and propulsive forces and MM of the lower-limbs were examined. Left-to-right peak forces were calculated as a percentage by the force plate software as ((left - right) / (left + right)) * 100. A fat-free mass asymmetry variable was manually calculated using this same formula. For both variables, a positive value indicated dominance of the left lower limb and a negative value indicated dominance of the right lower limb. The raw value of each asymmetry variable was used for correlations with other asymmetry variables while the absolute value of each asymmetry variable was used for correlations with variables that only allowed positive values. Alpha was set at 0.05. Normality was assessed with the Shapiro-Wilk test. Due to non-normality of some data, Spearman’s Rho was used for all correlational analysis. Alpha = 0.05. RESULTS: For the CMJ, peak propulsive force (PPF) was related to MM of the left (r = 0.689; p < 0.001) and right (r = 0.657; p < 0.001) lower-limb. The absolute value of the left-to-right peak landing force (PLF) was related to PLF (r = -0.351; p = 0.031). The absolute value of the left-to-right PPF was related to PPF (r = 0.322; p = 0.048). For the SJ, PPF was related to MM of the left lower-limb (r = 0.628; p < 0.001) and MM of the right lower-limb (r = 0.655; p < 0.001). Also for the SJ, left-to-right PPF was related to MM asymmetry (r = 0.386; p = 0.019). No relationships existed between jump height and any other variable for either jump. CONCLUSION: These results suggest that relationships between force asymmetries, overall force, and MM asymmetries in the lower-limbs during jumping are complex. Practically, they suggest that both force production and MM asymmetries are not clearly detrimental to jump performance.

Effects of a Competitive Soccer Match on Jump Performance and Interlimb Asymmetries in Elite Academy Soccer Players.

Bromley, T, Turner, A, Read, P, Lake, J, Maloney, S, Chavda, S, and Bishop, C. Effects of a competitive soccer match on jump performance and interlimb asymmetries in elite academy soccer players. J Strength Cond Res 35(6): 1707-1714, 2021-The purpose of this study was to investigate the effects of a competitive soccer match on jump performance and interlimb asymmetries over incremental time points during a 72-hour period. Fourteen elite adolescent players from a professional English category 3 academy performed single-leg countermovement jumps pre, post, 24-, 48-, and 72-hour post-match on a single force platform. Eccentric impulse, concentric impulse, peak propulsive force, jump height, peak landing force, and landing impulse were monitored throughout. Interlimb asymmetries were also calculated for each metric as the percentage difference between limbs. Significant negative changes (p < 0.05) in jump performance were noted for all metrics at all time points, with the exception of jump height. Interlimb asymmetries were metric-dependent and showed very large increases, specifically post-match, with a trend to reduce back toward baseline values at the 48-hour time point for propulsive-based metrics. Asymmetries for landing metrics did not peak until the 24-hour time point and again reduced toward baseline at 48-hour time point. This study highlights the importance of monitoring distinct jump metrics, as jump height alone was not sensitive enough to show significant changes in jump performance. However, interlimb asymmetries were sensitive to fatigue with very large increases post-match. More frequent monitoring of asymmetries could enable practitioners to determine whether existing imbalances are also associated with reductions in physical performance or increased injury risk.

The metabolic and mechanical consequences of altered propulsive force generation in walking

Older adults walk with greater metabolic energy consumption than younger for reasons that are not well understood. We suspect that a distal-to-proximal redistribution of leg muscle demand, from muscles spanning the ankle to those spanning the hip, contributes to greater metabolic energy costs. Recently, we found that when younger adults using biofeedback target smaller than normal peak propulsive forces (FP), they do so via a similar redistribution of leg muscle demand during walking. This alludes to an experimental paradigm that emulates characteristics of elderly gait independent of other age-related changes relevant to metabolic energy cost. Thus, our purpose was to quantify the metabolic and limb- and joint-level mechanical energy costs associated with modulating propulsive forces during walking in younger adults. Walking with larger FP increased net metabolic power by 47% (main effect, p = 0.001), which was accompanied by small by relatively uniform increases in hip, knee, and ankle joint power and which correlated with total joint power (R2 = 0.151, p = 0.019). Walking with smaller FP increased net metabolic power by 58% (main effect, p < 0.001), which was accompanied by higher step frequencies and increased total joint power due to disproportionate increases in hip joint power. Increases in hip joint power when targeting smaller than normal FP accounted for more than 65% of the variance in the measured changes in net metabolic power. Our findings suggest that walking with a diminished push-off exacts a metabolic penalty because of higher step frequencies and more total limb work due to an increased demand on proximal leg muscles.

Levodopa facilitates improvements in gait kinetics at the hip, not the ankle, in individuals with Parkinson's disease

Parkinson’s disease symptoms impair gait, limit mobility, and reduce independence. Levodopa improves muscle activation, strength, and coordination; thus, facilitating increased step length, but few studies have evaluated the underlying forces associated with medication-induced gait improvements. Here, we assess the effects of levodopa on gait kinetics in persons with Parkinson’s disease. Over two sessions, 13 participants with Parkinson’s disease walked on a treadmill while both optimally medicated and after a 12-hour medication withdrawal. Walking was analyzed for spatiotemporal parameters, ranges of motion, anterior-posterior ground reaction forces, joint torques, and powers using an instrumented treadmill and motion capture system. When on medication, participants increased gait speed by significantly improving step length (p = .009) and time (p = .004). Peak propulsive force (p = .001) and hip flexion torques (p = .003) increased with medication while hip extensor and ankle plantarflexor torques did not. While differences in joint power were not significantly different, the optimal medication condition showed medium to large effects, with the largest effect at the hip (dz = 0.84). Our findings suggest the underlying forces responsible for the increases in gait speed are primarily due to increases at the hip, with limited change at the ankle. Disproportionate use of muscle force may be a limiting factor for levodopa’s use as an intervention for walking. Future interventions should consider targeting force production deficits during gait in those with Parkinson’s disease.

Muscle metabolic energy costs while modifying propulsive force generation during walking

We pose that an age-related increase in the metabolic cost of walking arises in part from a redistribution of joint power where muscles spanning the hip compensate for insufficient ankle push-off and smaller peak propulsive forces (FP). Young adults elicit a similar redistribution when walking with smaller FP via biofeedback. We used targeted FP biofeedback and musculoskeletal models to estimate the metabolic costs of operating lower limb muscles in young adults walking across a range of FP. Our simulations support the theory of distal-to-proximal redistribution of joint power as a determinant of increased metabolic cost in older adults during walking.