Running Velocity Research Articles

Influence of shoe torsional stiffness on foot and ankle biomechanics during tennis forehand strokes

ABSTRACT Tennis shoe characteristics need to minimise the risk of athletes suffering ankle injuries and improve players’ feet performance. This study aims to evaluate the influence of shoe torsional stiffness on running velocity, stance duration, ground reaction forces and ankle biomechanics during two different tennis forehand runs and strokes. Ten right-handed advanced male tennis players performed two specific tennis forehand runs and strokes at maximal effort (a shuttle run with a defensive open stance forehand – SRDF and a lateral jab run with an offensive open stance forehand - JROF) with four different pairs of tennis shoes with different torsional stiffness. A force platform measured ground reaction forces (GRF). A motion capture system recorded the 3D trajectories of markers located on players’ anatomical landmarks. The minimum, maximum angle value, and range of motion were computed using inverse kinematics for each rotation axis of the right ankle. Normalised maximal ankle torques were also computed using inverse dynamics. Shoe torsional stiffness had no effect on running velocity, on stance duration and maximal values of GRF. Shoe torsional stiffness influenced forefoot inversion which was significantly higher for the most flexible shoes. For SRDF, the maximal ankle inversion angle was significantly and largely increased for the stiffest shoe. The stiffest shoe may put the ankle at a higher risk of lateral sprains during SRDF while it was not the case during JROF.

Longitudinal Assessment of Creatine Kinase, Creatine/Creatinineratio, and Myostatin as Monitoring Biomarkers in Becker Muscular Dystrophy.

The slow and variable disease progression of Becker muscular dystrophy (BMD) urges the development of biomarkers to facilitate clinical trials. We explored changes in 3 muscle-enriched biomarkers in serum of patients with BMD over 4-year time and studied associations with disease severity, disease progression, and dystrophin levels in BMD. We quantitatively measured creatine kinase (CK) using the International Federation of Clinical Chemistry reference method, creatine/creatinineratio (Cr/Crn) using liquid chromatography-tandem mass spectrometry, and myostatin with ELISA in serum and assessed functional performance using the North Star Ambulatory Assessment (NSAA), 10-meter run velocity (TMRv), 6-Minute Walking Test (6MWT), and forced vital capacity in a 4-year prospective natural history study. Dystrophin levels were quantified in the tibialis anterior muscle using capillary Western immunoassay. The correlation between biomarkers, age, functional performance, mean annual change, and prediction of concurrent functional performance was analyzed using linear mixed models. Thirty-four patients with 106 visits were included. Eight patients were nonambulant at baseline. Cr/Crn and myostatin were highly patient specific (intraclass correlation coefficient for both = 0.960). Cr/Crn was strongly negatively correlated, whereas myostatin was strongly positively correlated with the NSAA, TMRv, and 6MWT (Cr/Crn rho = -0.869 to -0.801 and myostatin rho = 0.792 to 0.842, all p < 0.001). CK showed a negative association with age (p = 0.0002) but was not associated with patients' performance. Cr/Crn and myostatin correlated moderately with the average annual change of the 6MWT (rho = -0.532 and 0.555, p = 0.02). Dystrophin levels did not correlate with the selected biomarkers nor with performance. Cr/Crn, myostatin, and age could explain up to 75% of the variance of concurrent functional performance of the NSAA, TMRv, and 6MWT. Both Cr/Crn and myostatin could potentially serve as monitoring biomarkers in BMD, as higher Cr/Crn and lower myostatin were associated with lower motor performance and predictive of concurrent functional performance when combined with age. Future studies are needed to more precisely determine the context of use of these biomarkers.

Match Loads May Predict Neuromuscular Fatigue and Intermittent-Running Endurance Capacity Decrement after a Soccer Match.

How the match-derived load metrics relate to post-match fatigue in soccer is scarcely researched. Thus, the aim of this study was to determine the associations between soccer match-related internal and external loads, neuromuscular performance decrease and intermittent-running endurance capacity decrement immediately post-match. Vertical jump (countermovement jump), straight-line sprinting (10- and 20-m sprint), change of direction ability (T-test) and intermittent-running endurance capacity (YO-YO intermittent recovery level 2) were measured one day before and immediately after a friendly match in male soccer players. During the match, players' internal and external loads were also monitored, including heart rate-derived indices, total distance at various speed thresholds, average running velocity, maximal running velocity, number of sprints and number of accelerations and decelerations at various intensity thresholds. The results show that match-induced fatigue was reflected on neuromuscular performance and intermittent-running endurance capacity immediately post-match (p &lt; 0.05). The quantification of percentage change of match external-load metrics, particularly accelerations and decelerations, provides a useful non-invasive predictor of subsequent neuromuscular fatigue status in soccer players immediately post-match (p &lt; 0.05). However, only internal load metrics present a practical application for predicting intermittent-running endurance capacity impairment (p &lt; 0.05). In summary, internal and external load metrics may allow for predicting the extent of acute fatigue, and variability between halves may represent a valuable alternative to facilitate the analysis of match-related fatigue both for research and applied purposes.

Running Velocity and Longitudinal Bending Stiffness Influence the Asymmetry of Kinematic Variables of the Lower Limb Joints.

Running-related limb asymmetries suggest specific sports injuries and recovery circumstances. It is debatable if running speed affected asymmetry, and more research is required to determine how longitudinal bending stiffness (LBS) affected asymmetry. The purpose of this study was to investigate the influence of running velocity and LBS on kinematic characteristics of the hip, knee, ankle, metatarsophalangeal joint (MTP) and the corresponding asymmetry. Kinematic (200 Hz) running stance phase data were collected bilaterally for 16 healthy male recreational runners (age: 23.13 ± 1.17, height: 175.2 ± 1.6 cm, body mass: 75.7 ± 3.6 kg, BMI: 24.7 ± 1.3 kg/m2) running on a force plate at three different velocities (10, 12 and 14 km/h) and three increasing-LBS shoes in a randomized order. The symmetry angle (SA) was calculated to quantify gait asymmetry magnitude at each running velocity and LBS. Changes in running velocity and LBS led to differences in kinematic variables between the hip, knee, ankle and MTP (p &lt; 0.05). Significant changes in SA caused by running velocity were found in the knee flexion angle (p = 0.001) and flexion angle peak velocity (p &lt; 0.001), ankle plantarflexion angle (p = 0.001) and plantarflexion angle peak velocity (p = 0.043) and MTP dorsiflexion angle (p = 0.001) and dorsiflexion angle peak velocity (p = 0.019). A significant change in the SA caused by LBS was found in the MTP dorsiflexion peak angle velocity (p = 0.014). There were interaction effects between running velocity and LBS on the MTP plantarflexion angle (p = 0.033) and plantarflexion angle peak velocity (p = 0.038). These findings indicate the existence of bilateral lower limb asymmetry. Meanwhile, it was proved that running velocity and LBS can influence the asymmetry of lower limb joints. Additionally, there was an interaction between running velocity and LBS on the asymmetry of the lower limb. These findings can provide some information for sports injuries, such as metatarsal stress fractures and anterior cruciate ligament injuries. They can also provide some useful information for running velocities and running shoes.

Interrelated but Not Time-Aligned Response in Myogenic Regulatory Factors Demethylation and mRNA Expression after Divergent Exercise Bouts.

DNA methylation regulates exercise-induced changes in the skeletal muscle transcriptome. However, the specificity and the time course responses in the myogenic regulatory factors DNA methylation and mRNA expression after divergent exercise modes are unknown. This study aimed to compare the time course changes in DNA methylation and mRNA expression for selected myogenic regulatory factors ( MYOD1 , MYF5 , and MYF6 ) immediately after, 4 h after, and 8 h after a single bout of resistance exercise (RE), high-intensity interval exercise (HIIE), and concurrent exercise (CE). Nine healthy but untrained males (age, 23.9 ± 2.8 yr; body mass, 70.1 ± 14.9 kg; peak oxygen uptake [V̇O 2peak ], 41.4 ± 5.2 mL·kg -1 ·min -1 ; mean ± SD) performed a counterbalanced, randomized order of RE (4 × 8-12 repetition maximum), HIIE (12 × 1 min sprints at V̇O 2peak running velocity), and CE (RE followed by HIIE). Skeletal muscle biopsies (vastus lateralis) were taken before (REST) immediately (0 h), 4 h, and 8 h after each exercise bout. Compared with REST, MYOD1 , MYF5 , and MYF6 , mean methylation across all CpGs analyzed was reduced after 4 and 8 h in response to all exercise protocols ( P < 0.05). Reduced levels of MYOD1 methylation were observed after HIIE and CE compared with RE ( P < 0.05). Compared with REST, all exercise bouts increased mRNA expression over time ( MYOD1 at 4 and 8 h, and MYF6 at 4 h; P < 0.05). MYF5 mRNA expression was lower after 4 h compared with 0 h and higher at 8 h compared with 4 h ( P < 0.05). We observed an interrelated but not time-aligned response between the exercise-induced changes in myogenic regulatory factors demethylation and mRNA expression after divergent exercise modes. Despite divergent contractile stimuli, changes in DNA methylation and mRNA expression in skeletal muscle were largely confined to the late (4-8 h) recovery period and similar between the different exercise challenges.

Kinematic Factors Associated with Hitting Hurdles During the Initial Phase of a 110-m Hurdle Race.

This study aimed to clarify the kinematic factors for the cause and effect of hitting hurdles during the initial phase of a 110-m hurdle run. Nine experienced male hurdlers participated in this study (body height: 1.74 ± 0.04 m, body mass: 67.4 ± 5.9 kg, age: 20.2 ± 1.4 years, personal best: 15.21 ± 0.47 s, seasonal best: 15.33 ± 0.55 s). Hurdlers undertook 12 trials of the initial phase of hurdling from the start to the second hurdle landing. Dual-sided sagittal plane motion was obtained from images from two high-speed cameras operating at 120 Hz. One ‘hit’ trial which had the largest horizontal displacement of markers fixed on the hurdle and one ‘non-hit’ trial which had the fastest time of hurdle clearance were extracted for each participant. Kinematic variables were compared between the two trials. Significantly lower height of the whole-body centre of mass at the take-off was found as a possible cause of hitting hurdles, caused by insufficient swing-up of the lead leg thigh. In contrast to conventional understanding, take-off velocity, take-off distance and the take-off angle were comparable between the ‘hit’ trial and ‘non-hit’ trial. Regarding the effect of hitting hurdles, it was observed that running velocity during hurdling was not substantially reduced. However, several characteristic movements were identified that might induce inefficient motion to re-accelerate running velocity during the following landing steps.

Hamstring Muscle Injuries and Hamstring Specific Training in Elite Athletics (Track and Field) Athletes.

Objective: We aimed to describe hamstring muscle injury (HMI) history and hamstring specific training (HST) in elite athletes. A secondary aim was to analyse the potential factors associated with in-championships HMI. Methods: We conducted a prospective cohort study to collect data before and during the 2018 European Athletics Championships. Injury and illness complaints during the month before the championship, HMI history during the entire career and the 2017–18 season, HST (strengthening, stretching, core stability, sprinting), and in-championship HMI were recorded. We calculated proportions of athletes with HMI history, we compared HST according to sex and disciplines with Chi2 tests or ANOVA, and analysed factors associated with in-championship HMI using simple model logistic regression. Results: Among the 357 included athletes, 48% reported at least one HMI during their career and 24% during the 2017–18 season. Of this latter group, 30.6% reported reduced or no participation in athletics’ training or competition at the start of the championship due to the hamstring injury. For HST, higher volumes of hamstring stretching and sprinting were reported for disciplines requiring higher running velocities (i.e., sprints, hurdles, jumps, combined events and middle distances). Five in-championship HMIs were recorded. The simple model analysis showed a lower risk of sustaining an in-championships HMI for athletes who performed more core (lumbo-pelvic) stability training (OR = 0.49 (95% CI: 0.25 to 0.89), p = 0.021). Conclusions: Our present study reports that HMI is a characteristic of the athletics athletes’ career, especially in disciplines involving sprinting. In these disciplines, athletes were performing higher volumes of hamstring stretching and sprinting than in other disciplines. Further studies should be conducted to better understand if and how HST are protective approaches for HMI in order to improve HMI risk reduction strategies.

Sex Differences In Marathon Performance Are Larger In The Past Decade Than Expected Physiologically

The sex difference in performance of marathon runners historically has been larger than explained by physiological differences, possibly reflecting lower participation of females (1). The number of female participants across all age groups has increased in recent decades, but it is unclear if the sex difference in performance has continued to diminish. PURPOSE: To determine the sex difference in performance in the New York City (NYC) marathon across age groups, and with the place of runner (1st-10th place), in the past decade and relative to earlier published data (1980-2010) (1). METHODS: Running times of the top 10 placed male and female finishers (5-year age groups) who competed in the NYC marathon (2009-2019) were retrieved from a public database (https://results.nyrr.org/races). Univariate ANOVA determined the sex difference in the mean running velocity; (% Δ males and females/males) across age groups and place. RESULTS: The sex difference in running velocity increased across age groups (p < 0.001). For 2015-2019, the 30-39-year olds had the smallest difference (12.9 ± 0.5%) and the 70-79 year olds the largest (22.9 ± 0.9%). Across all age groups, the sex difference in running velocity decreased across years from 22.0 ± 0.4% in 1980-84 to 16.1 ± 0.2% in 2005-2009 and plateaued for the subsequent decade. The largest drop was in the two older age groups (60-79 years, 36% to 21%) and the least for youngest (20-49 years, 18% to 12.5%). Across all age groups, the sex difference in running velocity for 1st placed runners was 15.9 ± 0.4 % and increased to 20.3 ± 0.3% for 10th (P < 0.001). The greatest increase in the sex difference (1st to 10th) was in the 70-79 age group (21.9 ± 1.5% to 31.6 ± 1.7%) and the least in the 40-49 age group (13.9 ± 0.6% to 17.8 ± 0.4%). CONCLUSION: The largest sex differences in marathon performance were within the older age groups and lower (slower)-placed runners. Across all age groups, the sex difference in performance plateaued in the past 15 years despite more female participants and the continued decrease in male:female participation ratios. These results also suggest that physiological and sociological factors that impact the sex difference in running velocity vary by age group. (1) Hunter SK, et al Med Sci Sports Exerc 45: 148-156, 2013.

Identifying Lower Extremity Static And Dynamic Asymmetries And Their Mutual Association In Male Professional Soccer

Between-limb asymmetries (BA) during standing, jumping and running are often discussed with physical performance and injury risk. It is reported that magnitude of BA is related to a specific movement commonly performed in certain sports (e.g. kicking ins soccer). Since those asymmetrical movements are repeatedly performed in some sports, it may gradually lead to a greater BA in both static and dynamic tasks over time. However, studies that focused on BA measure on both static and dynamic tasks are limited. Also, an association between static and dynamic tasks is understudied. PURPOSE: To investigate the BA in both static and dynamic tasks as well as examine a relationship between static and dynamic tasks among athletes who regularly performed asymmetrical movements. METHODS: A cross-sectional study was performed using 152 male professional soccer players of the highest Czech league. Kinematic running data were analyzed bilaterally using 3D treadmill at running velocity 12 km.h-1. Running asymmetry (RA) was evaluated and quantified using symmetry index (SI) for following variables: Impact Peak Force (IPF), Active Peak Force (APF), Impulse (I), Loading Rate (LR), Push off Rate (PR) and Step Length (SL). Postural stability (PSA) was evaluated by with a pressure platform as difference between legs during one-leg standing task (60 s). Pearson’s coefficient (r), coefficient of determination (R2) and effect size (d) were used for statistical assessment. RESULTS: The magnitude of BA varied by each variable with, with asymmetries <2% (APF = 1.36 ± 1.12 % [range: 5.50 %], I = 1.28 ± 1.07 % [range: 5.50 %], SL = 1.16 ± 1.38 % [range: 8.50 %] and greater asymmetries >5 % (LR = 6.33 ± 6.02 % [range: 38%], PSA = 7.42 ± 6.13 % [range: 28%]). Significant positive correlation (p < 0.05) has been found between APF vs. I (r = 0.44, R2 = 0.19, d = moderate), IPF vs. LR (r = 0.38, R2 = 0.14, d = moderate), APF vs. PR (r = 0.44, R2 = 0.19, d = moderate), PR vs. I (r = 0.35, R2 = 0.12, d = moderate), LR vs. I (r = 0.16, R2 = 0.03, d = small) and significant negative correlation between PSA vs. SL (r = - 0.18, R2 = 0.03, d = small). CONCLUSIONS: There were variabilities in the magnitudes of BA in both static and dynamic tasks. Limb asymmetry relationship between static and dynamic tasks were weak or none in this group of elite male professional soccer players.

A Numerical Study of a Pico Hydro Turbine

Pico hydro turbines are suitable for low head applications in power plants since their efficiency is more stable than other turbine types. In some situations, computational fluid dynamics (CFD) has also been utilized as well as experimental studies for the performance prediction of water turbines at a pico scale. Also, CFD methods are getting much closer to real conditions in terms of steady-state with moving references and transient domains with rotor movements. For this purpose, electricity production related to the flow in a PHT was investigated numerically. This study presents six degrees of freedom (6-DOF) and moving reference frame (MRF) methods to predict the maximum conditions of a pico scale two-dimensional turbine by comparing the torque and angular velocities on the runner based on the turbine output power of 1 W determined by an experimental study. Besides, the effect of the torque, angular velocity, tip speed ratio, and turbine body profile was investigated comprehensively. In this regard, MRF and 6-DOF methods were performed to validate and compare the numerical model with the experimental results. Also, the results obtained from 6-DOF and MRF methods were compared to experimental study. It is concluded that PHT is generating 0.3 W power under 6.47 rad/s angular velocity with 6-DOF method, however; this value corresponds to 31.4 rad/s angular velocity against 1 W with the MRF method. Also, the maximum velocity of the turbine was 6.1 m/s according to the simulation result. It is accepted that the turbine maximum velocity inlet was 0.53 m/s based on the experimental study. As a conclusion, numerical results for the pico hydro turbine were reasonable taking the experimental study into account. It is also concluded that there is a tip speed ratio of 2.36 with the MRF method and 0.48 with the 6-DOF method between water tangential velocity and runner velocity for the turbine model.

Reliability and Validity of the 30–15 Intermittent Field Test With and Without a Soccer Ball

ABSTRACTObjective: The purpose of this study was to examine the reliability and validity of the 30–15 Intermittent Field Test (30–15IFT) with and without a ball. Methods: Twenty-four collegiate female soccer players (19.46 ± 1.22 years; 167.01 ± 7.23 cm; 60.95 ± 7.84 kg) performed 1 trial of the Yo-Yo Intermittent Recovery (YYIR) test, 3 trials of the 30–15IFT, and 3 trials of the 30–15IFT with a ball (30–15IFT-B), separated by a minimum 48 hours. Maximal intermittent running velocity (VIFT), heart rate at exhaustion (HRpeak), and rating of perceived exertion (RPE) were collected. Results: Intraclass correlation coefficients (ICCs) between trials demonstrated good reliability during the 30–15IFT in VIFT (ICC = 0.88) and HRpeak (ICC = 0.89), in addition to the 30–15IFT-B VIFT (ICC = 0.83) and HRpeak (ICC = 0.87). VIFT was significantly reduced in 30–15IFT-B (15.82 km h−1) compared to 30–15IFT (17.52 km h−1; p < .001), regardless of trial. HR and RPE were significantly greater in 30–15IFT compared to 30–15IFT-B (p < .05). Estimated maximal oxygen consumption (VO2max) YYIR and estimated VO2max of 30–15IFT and 30–15IFT-B was very strongly (r = 0.82) and strongly (r = 0.68) correlated. Conclusion: The 30–15IFT is considered valid and reliable and the 30–15IFT-B was reliable in female soccer players.

Mathematical modeling of wear behavior and Abbott Firestone zones of 0.16C steel using response surface methodology

The effects of applied pressure and running velocity on wear behavior as well as Abbott Firestone zones of low carbon steel (0.16C) were evaluated using response surface methodology (RSM). At room temperature, three different pressures (0.5, 1.5, and 2.5 MPa) and three different velocities (1.5, 2.25, and 3 m/s) were used to conduct dry sliding wear trials utilizing the pin-on-disc method according to the experimental design technique (EDT). The experiments were created using central composite design (CCD) as a starting point. The relationship between input factors (pressure and velocity) and responses (wear rate and Abbott Firestone zones) of 0.16C steel was demonstrated using analysis of variance (ANOVA). The best models for wear rate as well as Abbott Firestone zones produced accurate data that could be estimated, saving time and cost. The results revealed that pressure had the greatest impact on the alloy’s dry sliding wear behavior of the two variables studied. In general, the predicted result shows close agreement with experimental results and hence created models could be utilized for the prediction of wear behavior and Abbott Firestone zones satisfactorily.

Intensified training before Olympic-distance triathlon in recreational triathletes: "Less pain, more gain".

To examine 1) the contribution of physiological performance variables to Olympic-distance (OD) triathlon performance, and 2) the links between an 8-wk intensified training plus competition preceding the main OD triathlon race and the changes in the physiological status in triathletes. An observational longitudinal study. Endurance performance variables during maximal incremental running and cycling tests, and average velocity during an all-out 400-m swimming performance test (V400) were assessed before (T1) and after (T2) the intensified training in 7 recreational-level triathletes. Overall main OD triathlon time was extremely largely (r = -0.94; P = 0.01) correlated with peak running velocity (PRV). Best correlation magnitude between exercise modes' partial race times and the corresponding specific physiological criterion tests was observed for swimming (r = -0.97; P<0.001). Improvement in V400 (2.9%), PRV (1.5%) and submaximal running blood lactate concentration (17%) was observed along the training period, whereas no changes were observed in the cycling endurance performance variables. Higher volume of training plus competition at high intensity zones during cycling, running and swimming were associated with lower improvements or declines in their corresponding exercise mode-specific criterion performance variables (r = 0.81-0.90; P = 0.005-0.037). Results indicate that: 1) PRV is highly associated with overall OD triathlon performance, and 2) spending much time at high relative intensities during swimming, cycling or running may lead, in a dose-response manner, to lower improvements or decreases on those exercise-specific physiological performance variables. This may favor the emergence of overreaching or diminished performance.

MATH MODEL OF RUNNING INDEX FOR EVALUATION AND CONTROL OF SPECIFIC EFFICIENCY AND TRACING THE FATIGUE LEVEL IN LONG-DISTANCE RUNNING

The aim of this case study was to develop and verify a math model of running index (RI) for evaluation and control of specific efficiency and tracing the fatigue level in long-distance running. The suggested RI was modeled on the basis of polynomial function between the running velocity and the change in heart rate frequency (V=f(HR)). The method was designed in such a way that the influence of denivelation of the terrain was removed when calculating RI. The research was done among 19 highly qualified athletes competing in long-distance running events (16 men and 3 women), with a mean age of 28 years (SD±8), BMI 20 (SD±2), maximum oxygen consumption 67 ml/min/kg (SD ±5). The participants in the research were subjected to two lab and two terrain surveys. In a period of one week after the testing, RI was traced and calculated on the basis of the data taken from the major training loads. The model was verified only for the studied subjects - highly qualified competitors in long-distance running. RI was tested for validity through comparing the values obtained from the lab and terrain tests. The obtained results showed there was no significant difference between the values of RI measured during the lab testing and the terrain testing compared to the values of the velocity of ventilatory and lactate anaerobic threshold (VAnT). The results from this research revealed that the suggested method for calculation of the running index is more accurate than the previous ones. This manuscript discusses the possible implications of this new method for measurement of RI. Future scientific research is needed to prove its efficiency and applicability in sports.

Variation in human 3D trunk shape and its functional implications in hominin evolution

This study investigates the contribution of external trunk morphology and posture to running performance in an evolutionary framework. It has been proposed that the evolution from primitive to derived features of torso shape involved changes from a mediolaterally wider into a narrower, and antero-posteriorly deeper into a shallower, more lightly built external trunk configuration, possibly in relation to habitat-related changes in locomotor and running behaviour. In this context we produced experimental data to address the hypothesis that medio-laterally narrow and antero-posteriorly shallow torso morphologies favour endurance running capacities. We used 3D geometric morphometrics to relate external 3D trunk shape of trained, young male volunteers (N = 27) to variation in running velocities during different workloads determined at 45–50%, 70% and 85% of heart rate reserve (HRR) and maximum velocity. Below 85% HRR no relationship existed between torso shape and running velocity. However, at 85% HRR and, more clearly, at maximum velocity, we found highly statistically significant relations between external torso shape and running performance. Among all trained subjects those with a relatively narrow, flat torso, a small thoracic kyphosis and a more pronounced lumbar lordosis achieved significantly higher running velocities. These results support the hypothesis that external trunk morphology relates to running performance. Low thoracic kyphosis with a flatter ribcage may affect positively respiratory biomechanics, while increased lordosis affects trunk posture and may be beneficial for lower limb biomechanics related to leg return. Assuming that running workload at 45–50% HRR occurs within aerobic metabolism, our results may imply that external torso shape is unrelated to the evolution of endurance running performance.

Motor guidance by long-range communication on the microtubule highway

Coupling of motor proteins within arrays drives muscle contraction, flagellar beating, chromosome segregation, and other biological processes. Current models of motor coupling invoke either direct mechanical linkage or protein crowding, which rely on short-range motor-motor interactions. In contrast, coupling mechanisms that act at longer length scales remain largely unexplored. Here we report that microtubules can physically couple motor movement in the absence of detectable short-range interactions. The human kinesin-4 Kif4A changes the run length and velocity of other motors on the same microtubule in the dilute binding limit, when approximately 10-nm-sized motors are much farther apart than the motor size. This effect does not depend on specific motor-motor interactions because similar changes in Kif4A motility are induced by kinesin-1 motors. A micrometer-scale attractive interaction potential between motors is sufficient to recreate the experimental results in a biophysical model. Unexpectedly, our theory suggests that long-range microtubule-mediated coupling affects not only binding kinetics but also motor mechanochemistry. Therefore, the model predicts that motors can sense and respond to motors bound several micrometers away on a microtubule. Our results are consistent with a paradigm in which long-range motor interactions along the microtubule enable additional forms of collective motor behavior, possibly due to changes in the microtubule lattice.

Research on deep learning model design technology of mobile terminal

Nowadays, object recognition and detection are inseparable from our lives which are related to various aspects in life. However, with the development of society and technology, the model of object detection become more and more complicated which affects the running velocity to some extent. In order to solve this problem, the key is to compress the model. On that note, the most important thing is to improve the running velocity without influencing the success rate of detection. To prune the mode, quantization is a low-cost way. Firstly, the object will be identified and detected by original model. After condensing model by pruning technology, run on this model to the same objects. Finally, it turns out that the model runs faster after pruning with little effect on the accuracy of object’s detection. Pruning minimizes model complexity, reduces the space needed for model storage, and also focuses on accelerating model training and prediction. It Can be applied during or after training.

Sex Differences in Performance and Depth of Field in the United States Olympic Trials.

Jobe, TK, Shaffer, HN, Doci, CL, and Gries, KJ. Sex differences in performance and depth of field in the United States Olympic trials. J Strength Cond Res 36(11): 3122-3129, 2022-Recently, there has been an increased discussion on the role of sex as a variable in human performance. Although there likely remains sociological factors, we can estimate biological sex differences in human performance by comparing finishing times in elite men and women. We sought to determine the effect of sex on running and swimming velocity and depth of field in events of varying lengths in the previous 25 years. Finishing times from United States Olympic trials in running events (100 m to marathon) and freestyle swimming (50-1,500 m) from 1996 to 2021 were collected. Sex differences in velocity were calculated for each year (trends), place (first through seventh), and depth of field (nth place/first place). Significance was set at p ≤ 0.05. Men were 9-13% faster than women in all running events (p ≤ 0.05). The 100-m dash (9%) had the lowest sex difference compared with races of longer distance (p ≤ 0.05). In swimming, men were faster in all events (6-12%, p ≤ 0.05), in which sex differences generally decreased with longer distances. Depth of field was similar between men and women in all running and swimming events. No differences in the analyzed variables were observed from 1996 to 2021. These data suggest that elite men are 9% faster in the 100 m compared with running races of longer distances (~12%). Sex differences in swimmers tended to get smaller as duration increased. Although participation and other sociological factors in these events may play a role, these sex differences warrant further discussion on the role of sex in athletic competition.

The Acute Effects of Heavy Sled Towing on Acceleration Performance and Sprint Mechanical and Kinematic Characteristics.

The aim of this study was to investigate the effects of heavy sled towing using a load corresponding to a 50% reduction of the individual theoretical maximal velocity (ranged 57–73% body mass) on subsequent 30 m sprint performance, velocity, mechanical variables (theoretical maximal horizontal force, theoretical maximal horizontal velocity, maximal mechanical power output, slope of the linear force–velocity relationship, maximal ratio of horizontal to total force and decrease in the ratio of horizontal to total force) and kinematics (step length and rate, contact and flight time). Twelve (n = 5 males and n = 7 females) junior running sprinters performed an exercise under two intervention conditions in random order. The experimental condition (EXP) consisted of two repetitions of 20 m resisted sprints, while in the control condition (CON), an active recovery was performed. Before (baseline) and after (post) the interventions, the 30 m sprint tests were analyzed. Participants showed faster 30 m sprint times following sled towing (p = 0.005). Running velocity was significantly higher in EXP at 5–10 m (p = 0.032), 10–15 m (p = 0.006), 15–20 m (p = 0.004), 20–25 m (p = 0.015) and 25–30 m (p = 0.014). No significant changes in sprint mechanical variables and kinematics were observed. Heavy sled towing appeared to be an effective post-activation potentiation stimulus to acutely enhance sprint acceleration performance with no effect on the athlete’s running technique.

An innovative energy harvesting backpack strategy through a flexible mechanical motion rectifier

This paper reports a fundamentally different strategy for realizing high-performance energy harvesting backpacks to effectively scavenge ultralow-frequency human body motions. The proposed backpack strategy is based on an innovative flexible mechanical motion rectifier (MMR) that consists of an inelastic strap, an elastic strap, a shaft with a double-layered plectrum, and a rotor. The flexible MMR first converts the human motion induced vibrations to the alternating spin of a shaft, and then enables the mono-directional spin of a rotor by a shaft through the stiffness self-adaptive plectrum. To examine the feasibility of the proposed strategy, an energy harvesting backpack was constructed with an array of the flexible MMR-based harvesters, and an electromechanical model of the backpack was also established and verified. Both simulations and experiments reveal the high output power of the backpack under various human travel velocities. Experiments show that, under a running velocity of 9 km/h, the backpack with a small payload of 3.6 kg can deliver high output power of 1.284 W. Under a walking velocity of 6 km/h, the electric energy generated by only one harvester of the backpack with a payload of 1.7 kg is sufficiently large for charging both a smart bracelet and a smart phone. This study demonstrates the feasibility of achieving high-performance energy harvesting backpacks with the flexible MMR for portable and wearable electronics.