The Influence of "Super-Shoes" and Foot Strike Pattern on Metabolic Cost and Joint Mechanics in Competitive Female Runners.

PURPOSE: The objective of this study is to assess the influence of "super-shoes" on metabolic cost and joint mechanics in competitive female runners and to understand how foot strike pattern may influence the footwear effects. METHODS: Eighteen competitive female runners ran four 5-min bouts on a force instrumented treadmill at 12.9 km·h -1 in 1) Nike Vaporfly Next% 2™ (SUPER) and 2) Nike Pegasus 38™ (CON) in a randomized and mirrored order. RESULTS: Metabolic power was improved by 4.2% ( P < 0.001; d = 0.43) and metatarsophalangeal (MTP) negative work ( P < 0.001; d = 1.22), ankle negative work ( P = 0.001; d = 0.67), and ankle positive work ( P < 0.001; d = 0.97) were all smaller when running in SUPER compared with CON. There was no correlation between foot strike pattern and the between-shoe (CON to SUPER) percentage change for metabolic power ( r = 0.093, P = 0.715). CONCLUSIONS: Metabolic power improved by 4.2% in "super-shoes" (but only by ~3.2% if controlling for shoe mass differences) in this cohort of competitive female runners, which is a smaller improvement than previously observed in men. The reduced mechanical demand at the MTP and ankle in "super-shoes" are consistent with previous literature and may explain or contribute to the metabolic improvements observed in "super-shoes"; however, foot strike pattern was not a moderating factor for the metabolic improvements of "super-shoes." Future studies should directly compare the metabolic response among different types of "super-shoes" between men and women.

Increasing Breast Support is Associated With a Distal-to-Proximal Redistribution of Joint Negative Work During a Double-Limb Landing Task.

Female athletes exhibit greater rates of anterior cruciate ligament injury compared with male athletes. Biomechanical factors are suggested to contribute to sex differences in injury rates. No previous investigation has evaluated the role of breast support on landing biomechanics. This study investigates the effect of breast support on joint negative work and joint contributions to total negative work during landing. Thirty-five female athletes performed 5 landing trials in 3 breast support conditions. Lower-extremity joint negative work and relative joint contributions to total negative work were calculated. Univariate analyses of variance were used to determine the effect of breast support on negative joint work values. Increasing levels of breast support were associated with lower ankle negative work (P < .001) and ankle relative contributions (P < .001) and increases in hip negative work (P = .008) and hip relative contributions (P < .001). No changes were observed in total negative work (P = .759), knee negative work (P = .059), or knee contributions to negative work (P = .094). These data demonstrate that the level of breast support affects lower-extremity biomechanics. The distal-to-proximal shift in negative joint work and relative joint contributions may be indicative of a more protective landing strategy for anterior cruciate ligament injuries.

Increasing Trunk Mass Evokes Lower Extremity Biomechanical Plasticity during Stair Descent.

The purpose of this study was to investigate the influence of simulated changes in body mass on lower extremity joint work and relative joint contributions during stair descent. Ten healthy recreationally active college-age participants performed five stair descent trials in each of five loading conditions: no added load and with an additional 5%, 10%, 15% and 20% of their body weight. Three-dimensional ankle, knee and hip joint powers were calculated using a six degree-of-freedom model in Visual3D (C-Motion Inc., Germantown, MD, USA). Sagittal plane joint work was calculated as the joint power curve integrated with respect to time during the period between initial contact and toe off. Prism 9.0 (GraphPad Inc., San Diego, CA) was used to perform univariate 1 × 5 repeated measures analyses of variance to determine the effect of added mass on absolute and relative joint work values for total and for each lower extremity joint independently. Increasing added mass was associated with greater total lower extremity negative work during the stair descent task (p < 0.001). At the ankle, increasing added mass was associated with increasing magnitudes of negative joint work. Increasing added mass was associated with greater relative contributions of the ankle and reduced knee contributions to total negative lower extremity joint work (p = 0.014 and p = 0.006). The current findings demonstrated increases in ankle joint contributions to total lower extremity work while knee joint contributions to total lower extremity work were reduced in response to increasing added mass.

Increasing breast support is associated with altered knee joint stiffness and contributing knee joint biomechanics during treadmill running.

Introduction: Greater breast support has been associated with improved running performance as measured by oxygen cost and running economy. Several candidate mechanisms have been proposed to underlie breast support-related improvements in running performance including increased knee joint stiffness. Greater knee joint stiffness has been associated with improved running performance (speed and metabolic cost), though the influence of breast support on knee joint stiffness has not been previously investigated. Therefore, the purpose of this study was to investigate the influence of increasing breast support on knee joint stiffness and its constituent components during treadmill running. Methods: Thirteen recreational runners performed a 3-min running bout at their preferred running velocity in each of three breast support conditions: bare chested (CON), low support (LOW) and high support (HIGH) sports bras. Three-dimensional kinematics and ground reaction forces were collected simultaneously using a 10-camera motion capture system (240 Hz, Qualisys Inc.) and instrumented treadmill (1,200 Hz, Bertec Inc.). Visual3D (C-Motion Inc.) was used to calculate knee joint excursions, moments, powers and work while custom software (MATLAB) was used to calculate knee joint stiffness and breast displacements during the stance phase of running in each experimental condition. A series of 1 × 3 repeated measures analysis of covariance with post-hoc t-tests was used to evaluate the effect of breast support on knee joint biomechanics during treadmill running. Results: Increasing levels of breast support were associated with greater knee joint stiffness (p = 0.002) as a result of smaller knee flexion excursions (p < 0.001). Increases in knee extension power (p = 0.010) were observed with increasing levels of breast support while no differences were observed in knee extension moments (p = 0.202) or work (p = 0.104). Conclusion: Greater breast support is associated with increased knee joint stiffness resulting from smaller joint excursions. These findings may provide insight into the biomechanical mechanisms underlying previously reported improvements in running performance including reduced oxygen consumption and greater running economy.

The Influence of Footwear Longitudinal Bending Stiffness on Running Economy and Biomechanics in Older Runners.

Purpose: This study assessed the effects of footwear longitudinal bending stiffness on running economy and biomechanics of rearfoot striking older runners. Methods: Nine runners over 60 years of age completed two running bouts at their preferred running pace in each of three footwear conditions: low (4.4 ± 1.8 N·m-1), moderate (5.7 ± 1.7 N·m-1), and high (6.4 ± 1.6 N·m-1) bending stiffness. Testing order was randomized and a mirror protocol was used (i.e., A,B,C,C,B,A). Expired gases, lower limb kinematics, and ground reaction forces were collected simultaneously and lower limb joint kinetics, running economy (i.e., VO2), leg stiffness, and spatio-temporal variables were calculated. Results: Running economy was not different among stiffness conditions (p = 0.60, p = 0.53 [mass adjusted]). Greater footwear stiffness reduced step length (p = 0.046) and increased peak vertical ground reaction force (p = 0.019) but did not change peak ankle plantarflexor torque (p = 0.65), peak positive ankle power (p = 0.48), ankle positive work (p = 0.86), propulsive force (p = 0.081), and leg stiffness (p = 0.46). Moderate footwear stiffness yielded greater peak negative knee power compared to low (p = 0.04) and high (p = 0.03) stiffness. Conclusions: These novel findings demonstrate that increasing footwear longitudinal bending stiffness using flat carbon fiber inserts does not improve running economy and generally does not alter lower limb joint mechanics of rearfoot strike runners over 60 years. Future studies should investigate how other footwear characteristics (e.g., midsole material, plate location, and sole curvature) influence economy and biomechanics in this population.

Influence of dynamic stretching on ankle joint stiffness, vertical stiffness and running economy during treadmill running.

The purpose of the present study was to investigate whether and how dynamic stretching of the plantarflexors may influence running economy. A crossover design with a minimum of 48 h between experimental (dynamic stretching) and control conditions was used. Twelve recreational runners performed a step-wise incremental protocol to the limit of tolerance on a motorised instrumented treadmill. The initial speed was 2.3 m/s, followed by increments of 0.2 m/s every 3 min. Dynamic joint stiffness, vertical stiffness and running kinematics during the initial stage of the protocol were calculated. Running economy was evaluated using online gas-analysis. For each participant, the minimum number of stages completed before peak O2 uptake (V̇O2peak) common to the two testing conditions was used to calculate the gradient of a linear regression line between V̇O2 (y-axis) and speed (x-axis). The number of stages, which ranged between 4 and 8, was used to construct individual subject regression equations. Non-clinical forms of magnitude-based decision method were used to assess outcomes. The dynamic stretching protocol resulted in a possible decrease in dynamic ankle joint stiffness (-10.7%; 90% confidence limits ±16.1%), a possible decrease in vertical stiffness (-2.3%, ±4.3%), a possibly beneficial effect on running economy (-4.0%, ±8.3%), and very likely decrease in gastrocnemius medialis muscle activation (-27.1%, ±39.2%). The results indicate that dynamic stretching improves running economy, possibly via decreases in dynamic joint and vertical stiffness and muscle activation. Together, these results imply that dynamic stretching should be recommended as part of the warm-up for running training in recreational athletes examined in this study.

The influence of surface and speed on biomechanical external loads obtained from wearable devices in rearfoot strike runners.

External load variables such as peak tibial acceleration (PTA), peak vertical ground reaction forces (GRF) and its instantaneous vertical loading rate (IVLR) may contribute to running injuries although evidence is conflicting given the influence of training load and tissue health on injuries. These variables are influenced by footwear, speed, surface and foot strike pattern during running. The purpose of this study was to assess the influence of four surfaces and two running speeds on external load variables in rearfoot strike (RFS) runners. Twelve RFS runners (confirmed with sagittal foot contact angle) completed a 2-min running bout on a treadmill and 50-m running bouts over the three surfaces (pavement, rubber track and grass) in standardised shoes at their preferred speed and 20% faster. PTA and vertical GRFs were collected using inertial measurement units and in-shoe force insoles. No interaction or surface effects were observed (p > 0.017). The faster speed produced greater axial PTA (+19.2%; p < 0.001), resultant PTA (+20.7%; p < 0.001), peak vertical GRF (+6.6%; p = 0.002) and IVLR (+16.5%; p < 0.001). These findings suggest that surface type does not influence PTA, peak vertical GRF and IVLR but that running faster increases the magnitude of these external loads regardless of surface type in RFS runners.

Greater Breast Support Is Associated With Reduced Oxygen Consumption and Greater Running Economy During a Treadmill Running Task.

Introduction: Breast pain is a major barrier to running for women. While breast support through the use of sports bras reduces breast-related discomfort, the effect of breast support on running performance is less understood. Therefore, the purpose of the current study was to evaluate the effect of greater breast support on oxygen consumption and running economy during a treadmill running task. Methods: Fifteen female recreational runners performed a 10-min treadmill running task at their preferred running speed in each of two sports bra conditions: low support and high support. Participants ran on an instrumented treadmill (1,200 Hz, Bertec) while indirect calorimetry was performed using a metabolic measurement system (100 Hz, TrueOne, ParvoMedics). Average VO2 (absolute and relative) from the third to 10th minutes was used to evaluate oxygen consumption. Running economy was calculated as the distance traveled per liter of oxygen consumed. Paired samples t-tests were used to compare mean oxygen consumption and running economy values between breast support conditions. Correlation analysis was performed to evaluate the relationship between breast size and change in running performance. Results: Greater breast support was associated with reductions in absolute (p < 0.001) and relative oxygen consumption (p < 0.001; LOW: 30.9 ± 7.1 ml/kg/min; HIGH: 28.7 ± 6.7 ml/kg/min). Greater breast support was associated with increases in running economy (p < 0.001; LOW: 88.6 ± 29.1 m/L O2; HIGH: 95.2 ± 31.1 m/L O2). No changes in temporospatial characteristics of running were observed including cadence (p = 0.149), step length (p = 0.300) or ground contact time (p = 0.151). Strong positive linear correlations were observed between the change in running performance metrics and breast size (Oxygen Consumption: p < 0.001, r = 0.770; Relative Oxygen Consumption: p < 0.001, r = 0769; Running Economy: p < 0.001, r = 0.807). Conclusions: Greater breast support was associated with reduced oxygen consumption and increased running economy. These findings demonstrate that greater breast support is not only associated with improved comfort but also improved running performance.

Greater Breast Support Alters Trunk and Knee Joint Biomechanics Commonly Associated With Anterior Cruciate Ligament Injury.

Objective: The female breast is a passive tissue with little intrinsic support. Therefore, women rely on external breast support (sports bras) to control breast motion during athletic tasks. Research has demonstrated that lower levels of breast support are associated with altered trunk and pelvis movement patterns during running, a common athletic task. However, no previous study has identified the effect of sports bra support on movement patterns during other athletic tasks including landing. Therefore, the purpose of this study was to examine the effects of breast support on trunk and knee joint biomechanics in female collegiate athletes during a double-leg landing task. Methods: Fourteen female collegiate athletes completed five double-leg landing trials in each of three different sports bra conditions: no support, low support, and high support. A 10-camera motion capture system (250 Hz, Qualisys, Goteburg, Sweden) and two force platforms (1,250 Hz, AMTI, Watertown, MA, USA) were used to collect three-dimensional kinematics and ground reaction forces simultaneously. Visual 3D was used to calculate trunk segment and knee joint angles and moments. Custom software (MATLAB 2021a) was used to determine discrete values of dependent variables including vertical breast displacement, knee joint and trunk segment angles at initial contact and 100 ms post-initial contact, and peak knee joint moments. A repeated measures analysis of covariance with post-hoc paired samples t-tests were used to evaluate the effect of breast support on landing biomechanics. Results: Increasing levels of breast support were associated with reductions in peak knee flexion (Right: p = 0.008; Left: p = 0.029) and peak knee valgus angles (Right: p = 0.011; Left: p = 0.003) as well as reductions in peak knee valgus moments (Right: p = 0.033; Left: p = 0.013). There were no changes in peak knee extension moments (Right: p = 0.216; Left: p = 0.261). Increasing levels of breast support were associated with greater trunk flexion angles at initial contact (p = 0.024) and greater peak trunk flexion angles (p = 0.002). Conclusions: Lower levels of breast support are associated with knee joint and trunk biomechanical profiles suggested to increase ACL injury risk.

A high fat western diet attenuates phasic dopamine release.

Natural rewards, such as food and social interaction, as well as drugs of abuse elicit increased mesolimbic dopamine release in the nucleus accumbens (NAc). Drugs of abuse, however, increase NAc dopamine release to a greater extent and are known to induce lasting changes on the functioning of the mesolimbic dopamine pathway. Less is known about the long-term effects of diet composition on this reward pathway. In the present study, two diets were compared: a higher-fat diet (Western Diet: WD) and a control diet (standard lab chow) on their effect on the mesolimbic dopamine system. Twenty male C57BL/6 J mice were placed on one of these diets at 7 weeks old. After twelve weeks on the diet, in vivo fixed potential amperometry was used to measure real-time stimulation-evoked dopamine release in the NAc of anesthetized mice before and after an i.p. injection of the dopamine transporter (DAT) inhibitor nomifensine. Results indicated that diet altered mesolimbic dopamine functioning. Mice that consumed the WD demonstrated a hypodopaminergic profile, specifically reduced baseline dopamine release and an attenuated dopaminergic response to DAT inhibition compared to the control diet group. Thus, diet may play a role in mediating dopamine-related behavior, disorders associated with dopamine dysfunction, and pharmacological treatments aimed at altering dopamine transmission.

Potential Predictors of Vertical Jump Performance: Lower Extremity Dimensions and Alignment, Relative Body Fat, and Kinetic Variables.

ABSTRACT: Daugherty, HJ, Weiss, LW, Paquette, MR, Powell, DW, and Allison, LE. Potential predictors of vertical jump performance: Lower extremity dimensions and alignment, relative body fat, and kinetic variables. J Strength Cond Res 35(3): 616-625, 2021-The association of structural and kinetic variables with restricted vertical jump (RVJ) displacement without and with added mass was examined in 60 men and women. Added mass (weighted vest) simulated a 5% increase in body fat (BF%). Independent variables included BF%, thigh length, and static Q-angle (Q-angles), and while performing RVJ, different expressions of frontal-plane knee angle (FPKA), dynamic Q-angle (Q-angled), vertical ground reaction force (vGRF), concentric vertical impulse (Iz), concentric rate of force development (CRFD), and vertical power (Pz). Variables having significant (p ≤ 0.05) negative correlations with RVJ displacement included BF% (r = -0.76) and Q-angles (r = -0.55). Those having significant (p ≤ 0.05) positive correlations with RVJ displacement included peak and average concentric Pz (r range = 0.74-0.81), peak and average concentric vGRF (r range = 0.46-0.67), Iz (r range = 0.32-0.54), thigh length (r = 0.31), minimum Q-angled (r = 0.31), and maximum FPKA (r = 0.28). Variables not associated (p > 0.05) with RVJ displacement included minimum and excursion FPKA (r = 0.11 and 0.23), maximum, excursion, and average Q-angled (r = 0.24, 0.11, and 0.22), and CRFD (r range = 0.19-0.24). A simple regression model predicted RVJ displacement (p = 1.00) for the simulated 5% increase in body fat. To maximize jumping performance, (a) high levels of body fat should be avoided, (b) peak and average Pz, vGRF, and Iz should be maximized through training, and (c) having a lower Q-angles is associated with better jumping ability.

Age and training volume influence joint kinetics during running.

Recently, we proposed the hypothesis that weekly running volume and preferred running pace may play a role in preserving ankle joint kinetics in middle-age runners as ankle joint kinetics were generally similar in young and middle-aged runners with similar running volume and preferred pace. To further address this hypothesis, we compared lower extremity joint kinetics between high and low training volume runners in both young and middle-aged groups. Joint kinetics calculated from 3D kinematic and ground reaction force data during over-ground running at 2.7 m·s-1 from young and middle-aged runners who ran low or high weekly volume were analyzed. A two-factor analysis of variance was used to compare joint kinetics between age and running volume groups. Positive hip work was greater in middle-aged compared to young runners (P = .005). Plantarflexor torque (P = .009) and positive ankle work (P = .042) were greater in young compared to middle-aged runners. Positive ankle work was also greater in the high compared to the low volume group (P = .021). Finally, age by volume interactions were found for knee extensor torque (P = .024), negative knee work (P = .018), and positive knee work (P = .019) but not for ankle and hip joint kinetics. These findings suggest less distal-to-proximal difference in positive joint work with high running volume in both young and middle-aged runners as a result of greater power generation at the ankle. Given the age main effects, our findings are also the first to suggest the age-related distal-to-proximal shift in joint kinetics appears in middle-aged runners.

Ground reaction force profiles during inclined running at iso-efficiency speeds.

While running provides an accessible form of cardiovascular stimulus, many runners report lower extremity musculoskeletal injuries. Additionally, runners who develop overuse injuries, such as tibial stress fractures, also have higher loading rates (LR) and impact forces. PURPOSE: Therefore, the purpose of this study was to investigate how uphill treadmill running at iso-efficient speeds (IES; a speed-incline combination having the same metabolic intensity as level running) influences impact LR, and peak vertical ground reaction forces (GRF). METHODS: Eleven collegiate distance runners completed 3 experimental running conditions (0%, 4%, and 8% treadmill inclination). During each running condition, the metabolic intensity was controlled by implementing an IES for each runner. RESULTS: All variables of interest were significantly reduced as treadmill incline increased (0% > 4% > 8%). CONCLUSION: Incline running is more metabolically demanding compared to level running at the same speed. But, if speed is controlled to maintain metabolic output, runners could decrease LR and peak vertical GRF while achieving the same metabolic training stimulus as level running.

Sex Differences in Ground Reaction Force Profiles of Ballet Dancers During Single- and Double-Leg Landing Tasks.

It is well known that sex differences exist in landing biomechanics in athletes, and these differences are purported to underlie a prevalence of traumatic knee injuries in females compared to males. However, it remains unknown if these differences also apply to artistic athletes such as dancers. The purpose of this study was to investigate sex differences in ground reaction forces (GRFs) between male and female dancers during single- and double-leg dance-specific landing movements. Fourteen pre-professional and professional ballet dancers (seven female and seven male) performed grand jeté (single-leg landing) and sauté (double-leg landing) jumps onto two force platforms. Visual3D was used to calculate the resulting GRF time-series, and MAT-LAB to select discrete variables of interest including peak vertical GRF, loading rate, landing duration, and vertical impulse. Paired t-tests were used to compare mean GRF variables between male and female dancers. During single-leg landing male dancers had smaller peak vertical GRFs (p < 0.01), greater time-to-peak GRF (p = 0.03), and smaller loading rates (p < 0.01) than female dancers. No differences were observed in vertical impulse during single-leg landing or in any variables during double-leg landing. These results indicate that sex differences in landing GRFs are most evident in single-leg landing and may underlie divergent injury rates in male and female dancers. Further investigation of relevant lower extremity biomechanics during single- and double-leg landing in male and female dancers should be conducted to identify the mechanisms underlying these distinct GRF profiles.

Influence of Prolonged Running and Training on Tibial Acceleration and Movement Quality in Novice Runners.

CONTEXT: Changes in lower limb loading and movement quality after prolonged running and training periods might influence injury risks in runners. OBJECTIVES: To assess (1) the effects of a single prolonged run and a 3-week running training program on peak tibial acceleration (PTA) during running and Functional Movement Screen (FMS) criterion tests, and (2) the relationship between running volume during the 3-week training program and changes in PTA and FMS scores after training. DESIGN: Case series. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten novice runners (age = 27 ± 7 years) with 15 ± 14 months of running experience, who ran on average 19.6 ± 4.8 km per week at a preferred pace of 7:05 ± 1:30 minutes per km. MAIN OUTCOME MEASURE(S): Participants completed a 30-minute submaximal prolonged treadmill run and 3-week training program with 25% increases in weekly running volume. Peak tibial acceleration and the deep-squat and active straight-leg-raise criterion FMS test scores were assessed before and after the prolonged run at enrollment and after the training program (ie, 3 testing sessions). RESULTS: No differences in PTA or FMS scores were observed among the 3 testing times. Although the changes in PTA (r = 0.57) and FMS aggregate score (r = 0.15) were not significantly correlated with training volume, training volume explained 32% of the variance in the PTA change from before to after training. CONCLUSIONS: Our findings suggest that tibial acceleration and movement quality were not influenced by a single submaximal-effort prolonged run or a 3-week training period. However, novice runners who have a greater increase in running volume might be more susceptible to training-related changes in tibial acceleration than those whose running volume is less.

Ankle kinetics and plantarflexor morphology in older runners with different lifetime running exposures.

Running promotes better cardiovascular health and has positive effects on the musculoskeletal system in older adults. However, older adults have lower ankle plantarflexor torques and positive powers during running, and exhibit changes in plantarflexor morphology than young adults. Since older runners who run as much as younger runners exhibit youthful ankle mechanical outputs, running exposure may preserve the locomotor factors that mediate running speed. The purpose of this study was to compare ankle mechanical output during running and plantarflexor morphological characteristics between older runners who have low or high lifetime running exposure. Ten older runners with low lifetime running exposure and nine older runners with high lifetime running exposure performed over-ground running trials at 3.0 m/s (±5%) while kinematic and ground reaction force (GRF) data were collected and used to compute joint angular kinetics. Right medial gastrocnemius morphological characteristics were assessed using ultrasonography at rest and during isometric contractions. Ankle torques, powers, and plantarflexor morphology were compared between groups. Older runners with different lifetime running exposures ran with similar ankle mechanical output (i.e. no effect of running exposure) (p > .05) and exhibited similar medial gastrocnemius morphology during isometric testing. The findings from this study demonstrate that lifetime running exposure does not appear to influence ankle mechanical output or plantarflexor morphology in middle-aged runners.

Lower Limb Joint Kinetics During Walking in Middle-Aged Runners With Low or High Lifetime Running Exposure.

Aging is associated with a distal-to-proximal shift in joint kinetics during walking. This plasticity of gait is amplified rather than attenuated in old adults with high physical capacity. Because running is associated with greater kinetic demands at the ankle, older individuals with more versus less lifetime running exposure may retain a larger proportion of their ankle kinetics. The purpose of the study was to compare lower-extremity joint kinetics during walking between middle-aged runners with high and low lifetime running exposure. Eighteen middle-aged runners (9 per group) participated. Joint kinetics were calculated from kinematic and ground reaction force data during overground walking at 1.3 m·s-1 and compared between groups. High exposure runners produced 50% greater positive hip work (P = .03; Cohen d = 1.02) during walking compared with low exposure runners, but ankle kinetics were not different between groups. No other differences in joint kinetics or kinematics were observed between groups. These findings suggest that the age-related increase in hip joint kinetics during walking could be a compensatory gait strategy that is not attenuated by lifetime running exposure alone. Finally, the amount of lifetime running exposure did not affect ankle kinetics during walking in middle-aged runners.

Baseline Postural Control and Lower Extremity Injury Incidence Among Those With a History of Concussion.

CONTEXT: Lower extremity musculoskeletal (LEMSK) injury may be more prevalent among those with a history of sport-related concussion (SRC). OBJECTIVE: To investigate the relationship between baseline postural control metrics and the LEMSK injury incidence in National Collegiate Athletic Association Division I student-athletes with a history of SRC. SETTING: National Collegiate Athletic Association Division I athletes. DESIGN: Cohort study. PATIENTS OR OTHER PARTICIPANTS: Of 84 total athletes (62 males), 42 had been previously diagnosed with an SRC, and 42 were matched controls based on age, sex, height, weight, and sport. MAIN OUTCOME MEASURE(S): During the preseason baseline evaluation, all participants performed 3 trials of eyes-open and eyes-closed upright quiet stance on a force platform. Medical charts were assessed for all the LEMSK injuries that occurred from preseason baseline to 1 year later. Center-of-pressure data in the anteroposterior and mediolateral directions were filtered before we calculated root mean square and mean excursion velocity; the complexity index was calculated from the unfiltered data. Factorial analysis-of-variance models were used to examine differences between groups and across conditions for root mean square; mean excursion velocity, complexity index, and tests of association to examine between-groups LEMSK differences; and logistic regression models to predict LEMSK. RESULTS: Concussion history and injury incidence were related in the SRC group (P = .043). The complexity index of the SRC group was lower with eyes closed (14.08 ± 0.63 versus 15.93 ± 0.52) and eyes open (10.25 ± 0.52 vs 11.80 ± 0.57) in the mediolateral direction than for the control participants (P < .05). Eyes-open root mean square in the mediolateral direction was greater for the SRC group (5.00 ± 0.28 mm) than the control group (4.10 ± 0.22 mm). Logistic regression models significantly predicted LEMSK only in control participants. CONCLUSIONS: These findings may suggest that LEMSK after SRC cannot be predicted from postural-control metrics at baseline.

Footwear and Sex Differences in Performance and Joint Kinetics During Maximal Vertical Jumping.

Smith, RE, Paquette, MR, Harry, JR, Powell, DW, and Weiss, LW. Footwear and sex differences in performance and joint kinetics during maximal vertical jumping. J Strength Cond Res 34(6): 1634-1642, 2020-This investigation examined the effects of footwear and sex on vertical jump displacement and joint power contributions. Twenty-three young adults with basketball experience performed 3 maximal countermovement vertical jumps in minimal and standard footwear. Ground reaction force and 3D kinematic data were collected during jumping. Footwear by sex analysis of variance for all dependent variables and effect sizes (d) was computed. An interaction effect showed that men produced greater lower-limb-positive work than women in standard footwear. Men jumped higher than women (d = 2.53) and produced greater peak ankle, knee and hip joint moments (d > 0.99), positive joint powers (d > 1.07) and, positive knee and hip joint work (d > 1.04) with no sex differences for negative joint powers and work (p > 0.05). Minimal footwear produced less peak-positive knee power (d = 0.27) and less positive ankle (d = 0.34) and knee (d = 0.21) joint work than standard footwear. Because negative joint power and work were similar between sexes, men may be better able to use the stretch-shortening cycle compared with women. Higher joint mechanical demands may provide a better vertical jumping training stimulus in standard compared with minimal footwear. Future studies should investigate footwear training effects on performance and joint mechanics during jumping.

Biomechanical Comparison of a New Dynamic Ankle Orthosis to a Standard Ankle-Foot Orthosis During Walking.

Patients who sustain irreversible cartilage damage or joint instability from ankle injuries are likely to develop ankle osteoarthritis (OA). A dynamic ankle orthosis (DAO) was recently designed with the intent to offload the foot and ankle using a distractive force, allowing more natural sagittal and frontal plane ankle motion during gait. To evaluate its efficacy, this study compared ankle joint kinematics and plantar pressures among the DAO, standard double upright ankle-foot orthosis (DUAFO), and a nonorthosis control (CON) condition in healthy adults during walking. Ten healthy subjects (26 ± 3.8 yr; 69.6 ± 12.7 kg; and 1.69 ± 0.07 m) walked on a treadmill at 1.4 m/s in three orthosis conditions: CON, DAO, and DUAFO. Ankle kinematics were assessed using a three-dimensional (3D) motion capture system and in-shoe plantar pressures were measured for seven areas of the foot. DAO reduced hallux peak plantar pressures (PPs) compared to CON and DUAFO. PPs under toes 2-5 were smaller in DAO than DUAFO, but greater in DUAFO compared to CON. Early stance peak plantarflexion (PF) angular velocity was smaller in DAO compared to CON and DUAFO. Eversion (EV) ROM was much smaller in DUAFO compared to CON and DAO. Early stance peak eversion angular velocity was smaller in DAO and much smaller in DUAFO compared to CON. This study demonstrates the capacity of the DAO to provide offloading during ambulation without greatly affecting kinematic parameters including frontal plane ankle motion compared to CON. Future work will assess the effectiveness of the DAO in a clinical osteoarthritic population.