Relation between soft tissue energy dissipation and leg stiffness in running at different step frequencies.

This study aims to investigate the relationship between soft tissue energy dissipation and leg stiffness during running. Eight recreational healthy male runners (age: 22.2 ± 1.0 years; height: 1.84 ± 0.03 m; mass: 73.7 ± 5.7 kg) were asked to run at different speeds and step frequencies. Their soft tissue energy dissipation was estimated by the difference between the total mechanical work of the body, measured as the work done to move the body centre of mass relative to the surroundings plus the work to move the limbs relative to the body centre of mass, and lower-limb joint work. A mass-spring model with an actuator was used to analyse the force-length curve of the bouncing mechanism of running. In this way, the stiffness and damping coefficient were assessed at each speed and step frequency. Pearson's correlations were used to describe the relationship between the deviation from the spring-mass model and soft tissue energy fluctuations. The soft tissue dissipation was found to be significantly influenced by step frequency, with both positive and negative work phases decreasing when step frequency increases. Moreover, deviation from a spring-mass model was positively associated with the amount of soft tissue dissipation (r > 0.6). The findings emphasize the substantial role of soft tissues in dissipating or returning energy during running, behaving in a damped-elastic manner. Also, we introduce a novel approach for evaluating the elastic rebound of the body during running. The insights gained may have broad implications for assessing running mechanics, with potential applications in various contexts.

The Determinants of Maximal Speed Adaptation During Preseason in Subelite Female Australian Rules Footballers.

PURPOSE: Maximal speed is an important physical-fitness attribute for female Australian footballers. The effects of sprint training, maximal strength, and technical training have been reported in laboratory studies. However, no study has determined the combined effect and relative contribution of these training modalities on maximal speed adaptation in situ. Therefore, the aim of this study was to determine the training factors affecting maximal speed adaptation during a preseason in subelite female Australian Rules footballers. METHODS: Maximal speed during field training, predicted 1-repetition maximum (1RM) for box squat and hip thrust, and sprint biomechanics were assessed during early and late preseason (∼9 wk apart) in 15 female subelite Australian Rules Football players (age 20 [3] y). On-field training volume and intensity (total distance, high-speed running, very-high-speed running, and maximal speed) were determined using a Global Positioning System. A multivariate regression model was used to determine the factors associated with changes in maximal speed across the preseason. RESULTS: The preseason training program had a small effect on maximal speed and large to very large effects on strength and sprint biomechanics. The multivariate regression with the greatest fit (P < .001, R2 = .939) included change in estimated 1RM box squat (ß = -0.63), total distance per week (ß = -0.55), and change in hip projection (ß = 0.16) as factors. Multivariate regression of biomechanical factors (P = .044, R2 = .717) and maximal strength factors (P = .003, R2 = .676) were also significant. CONCLUSION: The development of maximal speed across a preseason is dependent on (1) total distance per week, (2) maximal strength adaptation, and (3) sprint technique adaptation in female subelite Australian rules football players.

Does "Live High-Train Low and High" Hypoxic Training Alter Stride Mechanical Pattern During Repeated Sprints in Elite Team-Sport Players?

PURPOSE: We examined changes in stride temporal parameters and spring-mass model characteristics during repeated sprints following a 3-week period of "live high-train low and high" (LHTLH) altitude training in team-sport players. METHODS: While residing under normobaric hypoxia (≥14 h/d; inspired oxygen fraction [FiO2] 14.5%-14.2%) for 14 days, elite field hockey players performed, in addition to their regular field hockey practice in normoxia, 6 sessions (4 × 5 × 5-s maximal sprints; 25-s passive recovery; 5-min rest) under either normobaric hypoxia (LHTLH; FiO2 ∼14.5%, n = 11) or normoxia (live high-train low; FiO2 20.9%, n = 12). A control group (live low-train low; FiO2 ∼20.9%, n = 9) residing in normoxia without additional repeated-sprint training was included. Before (Pre) and a few days (Post-1) and 3 weeks (Post-2) after the intervention, stride mechanics were assessed during an overground repeated-sprint test (8 × 20 m, 20-s recovery). Two-way repeated-measures analysis of variance (time [Pre, Post-1, and Post-2] × condition [LHTLH, live high-train low, and live low-train low]) were conducted. RESULTS: Peak sprinting speed increased in LHTLH from Pre to Post-1 (+2.2% [2.0%]; P = .002) and Post-2 (+2.0% [2.4%]; P = .025), with no significant changes in live high-train low and live low-train low. There was no main effect of time (all P ≥ .062), condition (all P ≥ .771), or a significant time × condition interaction (all P ≥ .230) for any stride temporal variable (contact time, flight time, stride frequency, and stride length) or spring-mass model characteristics (vertical and leg stiffness). CONCLUSIONS: Peak sprinting speed improved in elite field hockey players following LHTLH altitude training, while stride mechanical adjustments to repeated overground sprints remained unchanged for at least 3 weeks postintervention.

Constant low-to-moderate mechanical asymmetries during 800-m track running.

Introduction: Modifications in asymmetry in response to self-paced efforts have not been thoroughly documented, particularly regarding horizontally-derived ground reaction force variables. We determined the magnitude and range of gait asymmetries during 800 m track running. Methods: Eighteen physical education students completed an 800 m self-paced run on a 200 m indoor track. During the run, vertical and horizontal ground reaction forces were measured at a sampling frequency of 500 Hz using a 5 m-long force platform system, with data collected once per lap. The following mechanical variables were determined for two consecutive steps: contact time and duration of braking/push-off phases along with vertical/braking/push-off peak forces and impulses. The group mean asymmetry scores were evaluated using the "symmetry angle" (SA) formula, where scores of 0% and 100% correspond to perfect symmetry and perfect asymmetry, respectively. Results: There was no influence of distance interval on SA scores for any of the nine biomechanical variables (P ≥ 0.095). The SA scores were ∼1%-2% for contact time (1.3 ± 0.5%), peak vertical forces (1.8 ± 0.9%), and vertical impulse (1.7 ± 1.0%). The SA scores were ∼3%-8% for duration of braking (3.6 ± 1.1%) and push-off (3.2 ± 1.4%) phases, peak braking (5.0 ± 2.1%) and push-off (6.9 ± 3.1%) forces as well as braking (7.6 ± 2.3%) and push-off (7.7 ± 3.3%) impulses. The running velocity progressively decreased at 300 m and 500 m compared to that at 100 m but levelled off at 700 m (P < 0.001). Discussion: There were no modifications in gait asymmetries, as measured at 200-m distance intervals during 800-m track running in physical education students. The 800 m self-paced run did not impose greater mechanical constraints on one side of the body. Experimental procedures for characterizing the gait pattern during 800 m track running could be simplified by collecting leg mechanical data from only one side.

Validity of Inertial Measurement Units to Measure Lower-Limb Kinematics and Pelvic Orientation at Submaximal and Maximal Effort Running Speeds.

Inertial measurement units (IMUs) have been validated for measuring sagittal plane lower-limb kinematics during moderate-speed running, but their accuracy at maximal speeds remains less understood. This study aimed to assess IMU measurement accuracy during high-speed running and maximal effort sprinting on a curved non-motorized treadmill using discrete (Bland-Altman analysis) and continuous (root mean square error [RMSE], normalised RMSE, Pearson correlation, and statistical parametric mapping analysis [SPM]) metrics. The hip, knee, and ankle flexions and the pelvic orientation (tilt, obliquity, and rotation) were captured concurrently from both IMU and optical motion capture systems, as 20 participants ran steadily at 70%, 80%, 90%, and 100% of their maximal effort sprinting speed (5.36 ± 0.55, 6.02 ± 0.60, 6.66 ± 0.71, and 7.09 ± 0.73 m/s, respectively). Bland-Altman analysis indicated a systematic bias within ±1° for the peak pelvic tilt, rotation, and lower-limb kinematics and -3.3° to -4.1° for the pelvic obliquity. The SPM analysis demonstrated a good agreement in the hip and knee flexion angles for most phases of the stride cycle, albeit with significant differences noted around the ipsilateral toe-off. The RMSE ranged from 4.3° (pelvic obliquity at 70% speed) to 7.8° (hip flexion at 100% speed). Correlation coefficients ranged from 0.44 (pelvic tilt at 90%) to 0.99 (hip and knee flexions at all speeds). Running speed minimally but significantly affected the RMSE for the hip and ankle flexions. The present IMU system is effective for measuring lower-limb kinematics during sprinting, but the pelvic orientation estimation was less accurate.

Preseason Vertical Center of Mass Displacement During Running and Bone Mineral Density Z-Score Are Risk Factors for Bone Stress Injury Risk in Collegiate Cross-country Runners.

OBJECTIVES: To (1) assess relationships between running biomechanics, bone health, and bone stress injuries (BSIs), and (2) determine which variables constitute the most parsimonious BSI risk model among collegiate cross-country runners. DESIGN: Prospective, observational cohort study. METHODS: Running gait and bone mineral density (BMD) data from healthy collegiate cross-country runners were collected at preseason over 6 seasons. A generalized estimating equation model with backward selection was used to develop the most parsimonious model for estimating BSI risk, controlling for sex, running speed, and prior BSI. The variables assessed were spatiotemporal, ground reaction force, and joint kinematics, based on previous literature. Quasi-likelihood under the independence model criterion values and R2 values were used to select the best-fitting model. RESULTS: Data from 103 runners were included in the analysis. The best-fitting model included vertical center of mass (COM) displacement and BMD z-score. Injury risk increased with greater vertical COM displacement (unit = 0.5 cm; relative risk [RR] = 1.14; 95% confidence interval [CI]: 1.01, 1.29; P = .04) and decreased with greater BMD z-score (unit = 0.5; RR = 0.83; 95% CI: 0.72, 0.95; P = .007). The model performed similarly when step rate was included instead of vertical COM displacement. CONCLUSION: Vertical COM displacement and BMD z-score contributed to the best model for estimating risk the risk of bone stress injury in cross-country runners. Step rate was also an important variable for assessing injury risk. J Orthop Sports Phys Ther 2023;53(12):1-8. Epub 20 October 2023. doi:10.2519/jospt.2023.11860.

Muscle inertial contributions to ankle kinetics during the swing phase of running.

Skeletal muscles have inertia that leads to inertial forces acting around joints. Although these inertial muscle forces contribute to joint kinetics, they are not typically accounted for in musculoskeletal models used for human movement biomechanics research. Ignoring inertial forces can lead to errors in joint kinetics, but how large these errors are in inverse dynamics calculations of common movements is yet unclear. We, therefore, examined the role of shank muscle inertia on ankle joint moments during the swing phase of running at different speeds. A custom musculoskeletal modelling and simulation platform was used to perform inverse dynamics with a model that either combined muscle mass in the total shank mass, or considered the gastrocnemius lateralis/medialis, soleus, and tibialis anterior muscles as separate masses from the shank. Ankle moments were considerably affected when muscles were modelled as separate masses, with a general shift towards reduced dorsiflexion and higher plantarflexion moments. Differences between both modelling conditions increased with running speed and ranged between 0.8 and 1.6 Nm (ankle moment profile root mean square error), 8-18 % (peak dorsiflexion moment difference) and 24-42 % (peak plantarflexion moment difference). Moreover, we observed a complex combination of inertial forces, especially those due to rotation and translation of the shank, in which the direction of inertial force changed during the swing phase. These results show that ignoring muscle inertia in musculoskeletal models can lead to under- or overestimations of structure-specific loads and thus erroneous study conclusions. Our results suggest that muscle inertial forces should be carefully considered when using musculoskeletal models.

Kinetic and Spatiotemporal Characteristics of Running During Regular Training Sessions for Collegiate Male Distance Runners Using Shoe-Based Wearable Sensors.

CONTEXT: Assessment of running mechanics has traditionally been conducted in laboratory settings; the advancement of wearable technology permits data collection during outdoor training sessions. Exploring changes in running mechanics across training-session types may assist runners, coaches, and sports medicine clinicians in improving performance and managing the injury risk. OBJECTIVE: To examine changes in running mechanics on the basis of routine training-session types. DESIGN: Descriptive observational study. SETTING: Field based, university. METHODS: Running mechanics data (ie, impact g, stride length, braking g, total shock g, cadence, and ground contact time) for National Collegiate Athletic Association Division I distance runners (n = 20 men) were collected using RunScribe sensors mounted to the laces during training sessions (long run [LR], interval run [IR], or recovery run [RR]) during a 1-week period. RESULTS: Repeated-measures analysis of covariance with Greenhouse-Geisser correction and training-session pace as a covariate indicated no statistically significant differences in spatiotemporal or kinetic measures across the 3 training-session types. Cadence and stride length were inversely related in all training sessions (LR: r = -0.673, P = .004; IR: r = -0.893, P < .001; RR: r = -0.549, P = .023). Strong positive correlations were seen between impact g and total shock in all training sessions (LR: r = 0.894, P < .001; IR: r = 0.782, P = < .001; RR: r = 0.922, P < .001). Ground contact time increased with stride length during LR training sessions (r = 0.551, P = .027) and decreased with braking g in IR training sessions (r = -0.574, P = .016) and cadence in RR training sessions (r = -0.487, P = .048). CONCLUSIONS: Running mechanics in collegiate distance runners were not statistically different among training-session types when training-session pace was controlled. The use of wearable technology provides a tool for obtaining necessary data during overland training to inform training and program design.

Asymmetries during repeated treadmill sprints in elite female Rugby Sevens players.

This study describes asymmetry in the main running mechanical variables during repeated treadmill sprints in elite female athletes and examines whether inter-limb differences in sprinting mechanics increase with fatigue. Eighteen elite female players (French national Rugby Sevens team) performed 8 × 5-s sprints (25-s rest) on an instrumented motorised sprint treadmill. The group mean 'symmetry angle' (SA) scores were ~1-2% for contact time (1.6 ± 0.6%), aerial time (2.1 ± 0.8%), step frequency (1.3 ± 0.5%) and step length (1.6 ± 0.6%). Mean vertical and horizontal forces, vertical and leg stiffness presented SA values of 1.7 ± 1.5%, 2.4 ± 1.2%, 2.6 ± 0.2% and 2.5 ± 0.2%, respectively. The SA scores were ~2-8% for duration of braking (6.9 ± 5.0%) and propulsive (6.5 ± 4.4%) phases, peak braking (6.5 ± 2.5%) and propulsive (1.6 ± 0.9%) forces as well as net (5.8 ± 5.6%), braking (7.7 ± 5.3%) and propulsive (2.7 ± 1.6%) impulses. However, there was no influence of sprint repetition number on SA scores for tested variables (P > 0.05). In elite female Rugby Sevens players, there was no noticeable difference in asymmetries for the great majority of stride mechanical variables during repeated treadmill sprints.

Mechanical asymmetries remain low-to-moderate during 30 min of self-paced treadmill running.

Introduction: We characterized the magnitude and range of gait asymmetry during self-paced treadmill running. Methods: On an instrumented treadmill, twelve trained runners (11 males, 1 female) completed a 30-min self-paced run, during which participants were instructed to cover the most distance possible. Ground reaction force recordings at a constant velocity corresponding to 70% of their maximal aerobic velocity (13.3 ± 0.8 km.h-1) allowed for the measurement of running kinetics and kinematics, as well as the calculation of spring-mass characteristics at the beginning, middle, and end of the run (minutes 1, 14, and 29, respectively). Group mean asymmetry scores were assessed using the "symmetry angle" (SA) formulae, where scores of 0% and 100% represent perfect symmetry and perfect asymmetry, respectively. Results: There was no time effect on SA scores for any of the 13 biomechanical variables (p ≥ 0.128). Mean SA scores were <2.5% for contact time (0.8% ± 0.7%), flight time (1.4% ± 0.6%), step frequency (0.7% ± 0.3%), duty factor (0.7% ± 0.3%), duration of braking (1.3% ± 0.7%) and push-off phases (0.9% ± 0.8%), as well as peak braking (2.3% ± 1.3%) and push-off forces (1.4% ± 0.9%). Mean SA scores were ≥2.5% for peak vertical loading rate (3.1% ± 1.7%), mean vertical loading rate (3.4% ± 2.1%), peak vertical forces (2.9% ± 2.2%), as well as vertical stiffness (5.2% ± 3.5%) and leg stiffness (2.5% ± 1.5%). Conclusion: Throughout a 30-min running time trial, there were consistently low-to-moderate mechanical asymmetries for spatiotemporal variables, kinetics, and spring-mass model characteristics. This suggests that trained runners maintained relatively even strides during the self-paced treadmill run, with lower extremities behaving similarly when controlling for velocity.

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.

Reversing the Mismatch With Forefoot Striking to Reduce Running Injuries.

Recent studies have suggested that 95% of modern runners land with a rearfoot strike (RFS) pattern. However, we hypothesize that running with an RFS pattern is indicative of an evolutionary mismatch that can lead to musculoskeletal injury. This perspective is predicated on the notion that our ancestors evolved to run barefoot and primarily with a forefoot strike (FFS) pattern. We contend that structures of the foot and ankle are optimized for forefoot striking which likely led to this pattern in our barefoot state. We propose that the evolutionary mismatch today has been driven by modern footwear that has altered our footstrike pattern. In this paper, we review the differences in foot and ankle function during both a RFS and FFS running pattern. This is followed by a discussion of the interaction of footstrike and footwear on running mechanics. We present evidence supporting the benefits of forefoot striking with respect to common running injuries such as anterior compartment syndrome and patellofemoral pain syndrome. We review the importance of a gradual shift to FFS running to reduce transition-related injuries. In sum, we will make an evidence-based argument for the use of minimal footwear with a FFS pattern to optimize foot strength and function, minimize ground reaction force impacts and reduce injury risk.

Constant low-to-moderate mechanical asymmetries during a treadmill graded exercise test.

This study describes asymmetry in key mechanical variables during a treadmill-based, running graded exercise test (GXT). Twenty-one recreationally trained male runners completed a continuous, maximal GXT on an instrumented treadmill, starting at 9 km.h-1 with speed increases of +0.5 km.h-1 every 30 s, for the determination of ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (MAX). Ground reaction forces were recorded continuously and subsequently averaged from 10 consecutive steps corresponding to VT, RCP and MAX intensity stages (13.4 ± 1.2 km.h-1, 16.0 ± 1.6 km.h-1 and 18.2 ± 1.5 km.h-1, respectively). Asymmetry scores were assessed from the "symmetry angle" (SA) formulae, where a score of 0%/100% indicates perfect symmetry/asymmetry; these were then compared between the three intensity stages. There was no influence of exercise intensity on SA scores for any of the sixteen biomechanical variables (P > 0.222). The group mean SA scores did not exceed 1.5% for spatio-temporal variables (contact time, aerial time, frequency and step length). There were larger mean SA scores for mean loading rate (3.7 ± 2.7%) and most spring-mass model variables (vertical stiffness: 2.2 ± 1.6% and leg stiffness: 1.7 ± 1.4%). The SA scores were ∼1.0-3.5% for braking and propulsive phase durations, peak forces, and resulting impulses. Lower extremities behave similarly at submaximal and maximal intensities during GXT, indicating that runners maintained relatively even strides as intensity increased. However, practitioners must be careful not to infer the presence of asymmetry during GXT based on a single variable, given the lower SA scores for spatio-temporal parameters.Highlights Our comprehensive list of sixteen mechanical variables provides a mechanical norm of expected asymmetry during treadmill graded exercise testing for recreationally trained runners.The stride pattern across submaximal and maximal exercise intensities remains consistent between limbs, with mechanical asymmetries being more individual-specific than intensity stage-dependent.Low to moderate asymmetry is a natural phenomenon in recreationally trained runners during treadmill graded exercise testing; notwithstanding, asymmetry scores appear inconsistent between mechanical parameters.

Asymmetry in sprinting: An insight into sub-10 and sub-11 s men and women sprinters.

We assessed sprint mechanical asymmetry in world-class competitors and evaluated whether inter-limb sex-based differences in sprinting mechanics exist. The eight finalists in the men's and women's 100 m events at the 2017 IAAF World Championships were studied. Five high-speed cameras (150 Hz) were used to capture two consecutive steps of the whole body between 47.0 m and 55.5 m from the start, while four additional cameras (250 Hz) focussed on the lower extremities. A total of 33 spatio-temporal, touchdown and toe-off joint angles, and horizontal and vertical foot velocity parameters were extracted through three-dimensional analysis. Group mean asymmetry scores were assessed using the symmetry angle (SA) where scores of 0% and 100% represent perfect symmetry and perfect asymmetry, respectively. Although considered generally low (SA <3% for 22 out of 33 parameters), the magnitude of mechanical asymmetry varied widely between sprinters of the same sex. However, there was no mean SA scores difference between men and women for any stride mechanical parameters (all p ≥ 0.064). Asymmetry scores were inconsistent between parameters and phases (touchdown vs toe-off instants), and sprinting mechanics were generally not related to asymmetry magnitudes. In summary, low to moderate asymmetry is a natural phenomenon in elite sprinting. Asymmetry was inconsistent between parameters and competitors during near maximum velocity running, yet mean values for a given parameter generally did not differ between sexes. Sprinters' performances were not related to their SA scores.

Running power: lab based vs. portable devices measurements and its relationship with aerobic power.

In recent years, different companies have developed devices that estimate "running power". The main objective of this paper is to evaluate the effect of running speed on aerobic and running powers measured using force plates and by different devices. The second objective is to evaluate the relationship between aerobic power and running powers measured using force plates and by different devices. We enrolled 11 subjects in the study, they performed 5-min running trials at 2.22, 2.78, 3.33, 3.89 and 4.44 m/s respectively on a force-measuring treadmill while we collected metabolic data. We calculated running power as the dot product of ground reaction force and velocity of the centre of mass and compared it to the running power estimates of three devices: Skillrun (Technogym), Stryd Summit Powermeter (Stryd) and Garmin HRM-Run (Garmin). We found statistically significant linear correlations with running powers measured by all devices and running speed. Although absolute running power measurements were different among devices, an increase of 1 m/s in running speed translated to an increase of 0.944 W/kg in running power (p < 0.001). We found statistically significant linear correlations with running powers measured by all devices and aerobic power, in particular: as aerobic power increases by 1 W/kg, running power increases by 0.218 W/kg for all devices (p < 0.001). For level treadmill running, across speeds, running power measured by commercially available devices reflects force-based measurements and it can be a valuable metric, providing quasi real-time feedback during training sessions and competitions.HighlightsWe evaluated the effect of running speed on aerobic and running powers measured using force plates and by different devices.We also compared the relationship between aerobic power and running powers measured using force plates and by different devices.We found statistically significant linear correlations with running powers measured by all devices and aerobic power, in particular: as aerobic power increases by 1 W/kg, running power increases by 0.218 W/kg for all devices.For level treadmill running, across speeds, running power measured by commercially available devices reflects force-based measurements and it can be a valuable metric, providing quasi real-time feedback during training sessions and competitions.

Detecting mechanical breakpoints during treadmill-based graded exercise test: Relationships to ventilatory thresholds.

BACKGROUND: While changes in cardio-respiratory variables during graded exercise tests (GXTs) are well described, less is known about running mechanical alterations. PURPOSE: We determined mechanical breakpoints during GXT and compared their temporal location with thresholds in ventilation. METHODS: Thirty-one recreational male runners completed continuous GXT on an instrumented treadmill, starting at 2.5 m.s-1 with velocity increases of +0.14 m.s-1 every 30 s. Subsequently, the first and second ventilatory thresholds (VT1 and VT2) were determined from expired gases. Spatio-temporal and antero-posterior force variables, and spring-mass model characteristics were averaged for each stage. Mechanical breakpoints were detected using a linear fit process that partitioned the timeseries into two regions and minimised the error sum of squares. All measurements were normalised to % GXT duration for subsequent comparisons. RESULTS: Fifteen out of 16 mechanical variables (all except leg stiffness) displayed breakpoints occurring between 61.9% and 82.3% of GXT duration; these occurred significantly later than VT1 (46.9 ± 6.4% of GXT duration, p < .05). Mechanical breakpoints for eight variables (step frequency, aerial time, step length, peak push-off force, braking impulse, peak vertical force, maximal downward vertical displacement and leg compression) occurred at a time point not different to VT2 (75.3 ± 6.2% of GXT duration; all p > .05). Relationships between mechanical breakpoints and either VT1 or VT2 were weak (all r < 0.25). CONCLUSION: During treadmill GXT, breakpoints can be detected for the vast majority of mechanical variables (except leg stiffness), yet these are not related with ventilatory thresholds.

Influence of lower limb dominance on mechanical asymmetries during high-speed treadmill running.

We determine whether mechanical asymmetries differ between dominant and non-dominant legs at fast treadmill speed. Stride temporal variables, derived from high-speed camera recordings, allowed to estimate leg and vertical stiffness through the sine-wave method in 31 uninjured males during treadmill running at 6.67 m.s-1. Lower limb dominance was determined by the triple-jump test. The asymmetry was expressed as dominant-non-dominant and indexed by the absolute asymmetry index (ASI). The lowest and highest mean ASI values were detected for contact time (1.69%) and flight time (5.66%), respectively; ASI values for spring-mass characteristics (2.6% ≤ leg and vertical stiffness, peak vertical force, change in vertical leg length and centre of mass vertical displacement ≤ 4.7%) were within this range. Inter-subject variability in ASI varied substantially among the seven analysed variables with larger and smaller range of variability in ASI found for flight time (0-16.56%) and contact time (0-3.47%), respectively. Because the magnitude of group mean ASI appears inconsistent among stride temporal and spring-mass characteristics, different biomechanical variables should not be used interchangeably to assess laterality effects at fast treadmill speed. The widespread ASI range also indicates that using a 'fixed cut-off' threshold is an arbitrary approach.

Roller Massage Prior to Running Does Not Affect Gait Mechanics in Well-Trained Runners.

CONTEXT: Understanding if roller massage prior to a run can mitigate fatigue-related decrements in muscle force production during prolonged running is important because of the association between fatigue and running-related injury. OBJECTIVE: The authors investigated whether a bout of roller massage prior to running would (1) mitigate fatigue-related increases in vertical average load rate and free moment of the ground reaction force of running and (2) mitigate decreases in maximal countermovement jump height. DESIGN: Repeated-measures study. SETTING: Laboratory. PARTICIPANTS: A total of 14 recreational endurance athletes (11 men and 3 women) volunteered for the study. INTERVENTIONS: A 12.5-minute foam roller protocol for the lower extremities and a fatiguing 30-minute treadmill run. MAIN OUTCOME MEASURES: Vertical average load rate, free moment, and maximal jump height before (PRE) and after (POST) the fatiguing treadmill run on separate experimental days: once where participants sat quietly prior to the fatiguing run (REST) and another where the foam roller protocol was performed prior to the run (ROLL). RESULTS: A 2-way multiple analysis of variance found no significant differences in vertical average load rate, free moment, and jump height between PRE/POST times in both REST/ROLL conditions. CONCLUSIONS: The authors concluded that recreational endurance athletes maintain running mechanics and jump performance after a fatiguing run regardless of prerun roller massage and may not rely on prerun roller massage as a form of injury prevention.

Gait asymmetries during perceptually-regulated interval running in hypoxia and normoxia.

This study aimed to characterise bilateral asymmetry in running mechanics during perceptually regulated, high-intensity intermittent running in hypoxia and normoxia and examines whether inter-limb differences in running mechanics are modified between and within intervals. Nineteen trained runners completed 4 × 4-min treadmill running bouts (3-min passive recoveries) at a perceived rating exertion of 16 on the 6-20 Borg scale in either hypoxic (FiO2 = 0.15) or normoxic (FiO2 = 0.21) conditions. Ground reaction force recordings at constant velocity (group average: 14.8 ± 1.9 km/h) allowed measurement of running kinetics/kinematics and calculation of spring-mass model characteristics at the beginning and the end of each 4-min interval. Lower limb asymmetry was assessed from the 'symmetry angle' (SA) score. There were no between intervals (P > 0.087), within intervals (P > 0.076) or FiO2 (P > 0.128) differences in SA scores for any of the 16 biomechanical variables. Mean SA scores were lower than 1.5% for spatio-temporal variables, ~1.5-3% for braking and push-off phase durations, peak forces and impulses and ~4-6% for mean loading rate and vertical stiffness. With preserved lower limb asymmetries both between and within intervals and with additional hypoxia, trained runners completing perceptually regulated interval treadmill runs may anticipate a maintained performance without heightened injury risk.

Running mechanics and leg muscle activity patterns during early and late acceleration phases of repeated treadmill sprints in male recreational athletes.

PURPOSE: We determined whether running mechanics and leg muscle activity patterns for pre-activation (50 ms prior to foot contact) and loading (first half, second half and entire stance) phases vary between early, late and entire acceleration phases during repeated treadmill sprints. METHODS: Ten male athletes performed three sets of five 5-s sprint accelerations (25-s and 3-min recovery between sprints and sets, respectively) on an instrumented treadmill. Ground reaction forces and surface EMG data (root mean square values of vastus lateralis, rectus femoris, biceps femoris, gastrocnemius medialis, gastrocnemius lateralis and tibialis anterior muscles of the right leg) corresponding to early, late and entire acceleration (steps 2, 4 and 6; steps 8, 10 and 12; and all steps, respectively) have been compared. RESULTS: Independently of fatigue, vertical and horizontal forces, contact time, step length, and step frequency differed as running velocity increased over different sprint acceleration sections (all P < 0.05). For pre-activation, first half, second half and entire stance phases taken separately, each of the six studied muscles displayed specific main sprint number and analysis section effects (all P < 0.05). However, there was in general no significant interaction between sprint number and analysis section (all P > 0.27). CONCLUSION: During repeated treadmill sprints, ground reaction force variables and leg muscle activity patterns can vary between early, late and entire acceleration phases. Identification of neuro-mechanical adjustments across the gait cycle with fatigue, however, did not differ when considering all steps or only a few steps during the early or late acceleration phases.