Treadmill Running Trials Research Articles

Can Machine Learning Predict Running Kinematics Based on Upper Trunk GPS-Based IMU Acceleration? A Novel Method of Conducting Biomechanical Analysis in the Field Using Artificial Neural Networks

This study aimed to investigate whether running kinematics can be accurately estimated through an artificial neural network (ANN) model containing GPS-based accelerometer variables and anthropometric data. Thirteen male participants with extensive running experience completed treadmill running trials at several speeds. Participants wore a GPS device containing a triaxial accelerometer, and running kinematics were captured by an 18-camera motion capture system for each trial. Multiple multilayer perceptron neural network models were constructed to estimate participants’ 3D running kinematics. The models consisted of the following input variables: 3D peak accelerometer acceleration during foot stance (g), stance time (s), running speed (km/h), participant height (cm), leg length (cm), and mass (kg). Pearson’s correlation coefficient (r), root mean squared error (RMSE), and relative root mean squared error (rRMSE) showed that ANN models provide accurate estimations of joint/segment angles (mean rRMSE = 13.0 ± 4.3%) and peak segment velocities (mean rRMSE = 22.1 ± 14.7%) at key gait phases across foot stance. The highest accuracies were achieved for flexion/extension angles of the thorax, pelvis, and hip, and peak thigh flexion/extension and vertical velocities (rRMSE < 10%). The current findings offer sports science and medical practitioners working with this data a method of conducting field-based analyses of running kinematics using a single IMU.

Validity and reliability of the DANU sports system for walking and running gait assessment

Objective. Gait assessments have traditionally been analysed in laboratory settings, but this may not reflect natural gait. Wearable technology may offer an alternative due to its versatility. The purpose of the study was to establish the validity and reliability of temporal gait outcomes calculated by the DANU sports system, against a 3D motion capture reference system. Approach. Forty-one healthy adults (26 M, 15 F, age 36.4 ± 11.8 years) completed a series of overground walking and jogging trials and 60 s treadmill walking and running trials at various speeds (8–14 km hr−1), participants returned for a second testing session to repeat the same testing. Main results. For validity, 1406 steps and 613 trials during overground and across all treadmill trials were analysed respectively. Temporal outcomes generated by the DANU sports system included ground contact time, swing time and stride time all demonstrated excellent agreement compared to the laboratory reference (intraclass correlation coefficient (ICC) > 0.900), aside from ground contact time during overground jogging which had good agreement (ICC = 0.778). For reliability, 666 overground and 511 treadmill trials across all speeds were examined. Test re-test agreement was excellent for all outcomes across treadmill trials (ICC > 0.900), except for swing time during treadmill walking which had good agreement (ICC = 0.886). Overground trials demonstrated moderate to good test re-test agreement (ICC = 0.672–0.750), which may be due to inherent variability of self-selected (rather than treadmill set) pacing between sessions. Significance. Overall, this study showed that temporal gait outcomes from the DANU Sports System had good to excellent validity and moderate to excellent reliability in healthy adults compared to an established laboratory reference.

Metabolic power response to added mass on the lower extremities during running

BackgroundWearable exoskeletal devices can enhance locomotor performance, but their mass results in a metabolic penalty. Previous studies have quantified the metabolic cost of running with added mass on the feet, but less is known about the effects of adding mass to the thigh and shank segments. AimTo quantify the metabolic cost of running with additional leg mass. Methods15 participants (7 F, 8 M) completed treadmill running trials (3 m/s) normally and with lead mass (300–1350 g) attached to either the thigh, shank, or foot, bilaterally. We measured metabolic power using expired gas analysis. ResultsPer 1000 g of added mass per leg, gross metabolic power increased by approximately 16% (foot) and 11% (shank) for females which was slightly greater than the 11% and 8% increases for males, respectively. For thigh loading, metabolic power increased by just 4% per 1000 g in both sexes. ConclusionAdding mass more distally on the leg increases the metabolic cost of running to a greater extent. For the same absolute added mass on the foot or shank, metabolic power increases more in females.

Iron Absorption in Highly Trained Male Runners: Does it Matter When and Where You Eat Your Iron?

ABSTRACT Purpose We examined iron absorption and its regulation during two common scenarios experienced by endurance athletes. Our aims were to: (i) compare the effects of preexercise versus postexercise iron intake on iron absorption; and (ii) compare the impact of training at altitude (1800 m) on iron absorption preexercise. Methods Male runners (n = 18) completed three exercise trials over a 5-wk period, each preceded by 24 h of standardized low-iron diets. First, athletes completed two 60-min treadmill running trials at 65% V̇O2max at near sea-level (580 m). In a randomized order, preexercise and postexercise test meals labeled with 4 mg of 57Fe or 58Fe were consumed 30 min before or 30 min after exercise. Then, the same exercise trial was performed after living and training at altitude (~1800 m) for 7 d, with the labeled test meal consumed 30 min preexercise. We collected venous blood samples preexercise and postexercise for markers of iron status and regulation, and 14 d later to measure erythrocyte isotope incorporation. Results No differences in fractional iron absorption were evident when test meals were consumed preexercise (7.3% [4.4, 12.1]) or postexercise (6.2% [3.1, 12.5]) (n = 18; P = 0.058). Iron absorption preexercise was greater at altitude (18.4% [10.6, 32.0]) than at near sea-level (n = 17; P < 0.001) and hepcidin concentrations at altitude were lower at rest and 3 h postexercise compared with near sea level (P < 0.001). Conclusions In an acute setting, preexercise and postexercise iron absorption is comparable if consumed within 30 min of exercise. Preexercise iron absorption increases 2.6-fold at altitude compared with near sea-level, likely due to the homeostatic response to provide iron for enhanced erythropoiesis and maintain iron stores.

Joint kinematic and kinetic responses to added mass on the lower extremities during running

AimWe analyzed the biomechanical response (joint angles, moments, and powers) to running with added leg mass. These data may help guide the design of wearable locomotor assistive devices (i.e., exoskeletons), which are becoming more prevalent. Methods15 participants (7 females, 8 males) completed treadmill running trials (3m•s−1) normally and with lead mass (300–1350 g) attached to the thigh, shank, or foot, bilaterally. We quantified the lower limb biomechanics combining motion capture and ground reaction force data using standard inverse dynamics analysis. ResultsOnly moderate kinematic changes occurred in response to the distal added limb mass. Maximum hip flexion and maximum knee flexion angles during swing phase increased by approximately 9% and 6% respectively for each 1 kg added to each foot. However, adding even small masses made dramatic changes to the joint moments and powers, mostly during the swing phase. For example, adding 1 kg to each foot increased maximum joint moments by as much as 40% (knee extension in late swing) and maximum joint power by as much as 50% (hip generation in late swing). ConclusionLeg joint kinematics were largely conserved in response to adding mass to the legs. Adding mass to the leg distally increased joint power mainly at the knee and hip joints during the swing phase, whereas adding mass proximally mainly affected the ankle joint mechanics during the stance phase. These changes have implications for shoe designs, people who run with added mass on their legs for sport/strength training and for the design of wearable devices.

The Influence of Footwear Midsole Thickness on Running Economy and Frontal Plane Ankle Stability

Despite being an intricate part of advanced footwear technology, the impact of midsole thickness is not well understood. While some individuals have speculated an increased midsole thickness might bequeath an unfair performance advantage, others have suggested it may have a detrimental impact on frontal plane ankle stability. Therefore, the purpose of this study was to determine the influence of midsole thickness on running economy, and frontal plane ankle stability. Twenty one recreational runners (ten female, and eleven male) participated in this study, performing five-minute treadmill running trials in four footwear conditions. The footwear conditions were nearly identical except for their midsole thicknesses which ranged from 35- to 50-mm in increments of 5-mm. Midsole thickness was not found to influence the energetic cost of running however, it was found to decrease frontal plane ankle stability. Given these results World Athletic restrictions on midsole thickness may be unnecessary and worthy of reconsideration.

Equivalent running leg lengths require prosthetic legs to be longer than biological legs during standing

We aimed to determine a method for prescribing a standing prosthetic leg length (ProsL) that results in an equivalent running biological leg length (BioL) for athletes with unilateral (UTTA) and bilateral transtibial amputations (BTTA). We measured standing leg length of ten non-amputee (NA) athletes, ten athletes with UTTA, and five athletes with BTTA. All athletes performed treadmill running trials from 3 m/s to their maximum speed. We calculated standing and running BioL and ProsL lengths and assessed the running-to-standing leg length ratio (Lratio) at three instances during ground contact: touchdown, mid-stance, and take-off. Athletes with UTTA had 2.4 cm longer standing ProsL than BioL length (p = 0.030), but their ProsL length were up to 3.3 cm shorter at touchdown and 4.1 cm shorter at mid-stance than BioL, at 3–11.5 m/s. At touchdown, mid-stance, and take-off, athletes with BTTA had 0.01–0.05 lower Lratio at 3 m/s (p < 0.001) and 0.03–0.07 lower Lratio at 10 m/s (p < 0.001) in their ProsL compared to the BioL of NA athletes. During running, ProsL were consistently shorter than BioL. To achieve equivalent running leg lengths at touchdown and take-off, athletes with UTTA should set their running-specific prosthesis height so that their standing ProsL length is 2.8–4.5% longer than their BioL length, and athletes with BTTA should set their running-specific prosthesis height so that their standing ProsL lengths are at least 2.1–3.9% longer than their presumed BioL length. Setting ProsL length to match presumed biological dimensions during standing results in shorter legs during running.

Effects of compression running pants and treadmill running stages on knee proprioception and fatigue-related physiological responses in half-marathon runners.

Background: Knee injury is common in half-marathon runners, however, the effect of compression running pants on fatigue and knee proprioception remains unclear. Objectives: The study aims to investigate whether wearing compression running pants (CRP) and treadmill running stages affect knee proprioception and fatigue-related physiological responses during half-marathon running. Methods: Eighteen half-marathon runners completed two self-paced 21km treadmill running trials, once wearing CRP and once wearing loose running shorts (LRS). For each 21km run, RPE, heart rate, blood lactic acid, and knee flexion proprioception were assessed before starting, and after each 7km stage. Results: Data analysis revealed no difference between CRP and LRS conditions in heart rate, RPE, or blood lactic acid. Repeated measures ANOVA showed a significant garment condition main effect whereby wearing CRP was associated with higher knee proprioceptive acuity (p = 0.006). Polynomial trend analysis showed a significant linear downwards trend in proprioceptive acuity across the four measurement occasions (p = 0.048). Stage analysis showed that wearing CRP was associated with better knee proprioception at running distances of 14km (p = 0.007, 95%CI = -0.054, -0.010) and 21km (p = 0.016, 95%CI = -0.051, -0.006). Conclusion: Compression running pants provide an overall positive effect on knee proprioception, particularly after 14km and 21km, which may reduce the probability of knee injury. CRP had no significant effect on physiological measures in half-marathon running.

Partitioning The Work Of Breathing During Running And Cycling Using Optoelectronic Plethysmography

Work of breathing (B) derived from a single lung volume and pleural pressure is limited and does not fully characterize the mechanical work done by the respiratory musculature. It has long been known abdominal activation increases with increasing exercise intensity, yet the mechanical work done by these muscles is not reflected in B. Optoelectronic plethysmography (OEP) is a 3-dimentional motion analysis tool that measures the positions and displacements of reflective markers on the thorax and abdomen to calculate volume changes. Importantly, OEP permits an assessment of the ribcage and abdominal contribution to volume changes during breathing. PURPOSE: We sought to: (1) show the volumes measured using OEP (VCW) were comparable to volumes from flow integration (Vt) during cycling and running, and (2) to demonstrate that partitioned ribcage and abdominal volume from OEP could be utilized to quantify the mechanical work done by the ribcage (BRC) and abdomen (BAB) during exercise. METHODS: We fit 11 subjects (6 males/5 females; age, 26 ± 3 years; body mass, 73 ± 10 kg; height, 177 ± 6 cm; maximal oxygen uptake, 55.2 ± 9.8 ml/kg/min) with 89 reflective markers, and esophageal and gastric balloon catheters. Subjects completed an incremental cycling test to exhaustion and a series of submaximal treadmill running trials. RESULTS: We found good agreement between VCW vs. Vt during cycling (bias = 0.002) (p > 0.05) and running (bias = 0.016) (p > 0.05). From rest to maximal-exercise, BAB increased by 84% (range: 30-99%; BAB: 1 ± 1 J/min to 61 ± 52 J/min). The relative contribution of the abdomen increased from 17 ± 9% at rest to 26 ± 16% during maximal-exercise. CONCLUSION: Our study highlights and provides a quantitative measure of the role of the abdominal muscles during exercise. Incorporating the work done by the abdomen allows for a greater understanding of the mechanical tasks required by the respiratory muscles under physiologically relevant conditions such as exercise. Moreover, our approach could be used to gain insight into how the respiratory system functions under pathophysiological conditions and injury.

The Effects Of The Nike Vapor Fly 4% Shoes On Running Economy In Fatigued Female Runners

The Nike Vaporfly 4% shoe (VP) has been shown to improve running economy (RE) up to 4% in subelite male runners. Whether these improvements extend to other subject groups, such as female runners or fatigued runners, remains unknown. PURPOSE: The purpose of this study was to determine if trained female runners gain the same 4% improvement in RE as males and if the improvement is observed post-fatigue. METHODS: Nine well-trained collegiate female runners completed one session alternating between the VP and the control shoe, Nike Streaks (NS). Subjects performed three vertical jumps in each shoe on a force pad to determine jump height and estimate stored energy return from each shoe. Subjects then performed two, 5-min treadmill running trials at 6.7 mph using a metabolic cart to measure oxygen consumption. Mean oxygen uptake over the last two minutes of each trial was used to determine RE. Following the first jump and RE trials, subjects performed a 30-minute treadmill run at a self-selected speed to induce fatigue. Subjects then repeated the jump and RE trials in the alternative shoe order. RESULTS: Oxygen consumption in the VP was lower when compared to the NS by 3.7% (31.8 ± 3 vs 33.6 ± 3 ml/kg/min p < 0.05) pre-fatigue and by 2.5% (32.5 ± 3 vs 33.3 ± 3 ml/kg/min p < 0.05) in the fatigued state, which is less than the anticipated 4% benefit. The pre- and post-fatigue reductions in oxygen consumption while wearing the VP were significantly different indicating the benefit of wearing the VP attenuated over time. Jump height in the VP was higher pre-fatigue (44.0 ± 6 vs 43.2 ± 6 cm, p < 0.05) but was not different in the fatigued state (43.8 ± 7 vs 43.6 ± 7 cm, p > 0.05) when compared to NS. CONCLUSION: Female runners experienced a similar improvement in RE while wearing the VP when compared to previous studies, however this improvement dropped to 2.7% following a relatively short fatiguing run. Thus, improvements in RE from the VP shoes may not extend through the entire duration of some running events in certain athletes.

Dietary Intake and Gastrointestinal Integrity in Runners Undertaking High-Intensity Exercise in the Heat.

Gastrointestinal disturbances are one of the most common issues for endurance athletes during training and competition in the heat. The relationship between typical dietary intake or nutritional interventions and perturbations in or maintenance of gut integrity is unclear. Twelve well-trained male endurance athletes (peak oxygen consumption = 61.4 ± 7.0ml·kg-1·min-1) completed two trials in a randomized order in 35 °C (heat) and 21 °C (thermoneutral) conditions and kept a detailed nutritional diary for eight consecutive days between the two trials. The treadmill running trials consisted of 15min at 60% peak oxygen consumption, 15min at 75% peak oxygen consumption, followed by 8 × 1-min high-intensity efforts. Venous blood samples were taken at the baseline, at the end of each of the three exercise stages, and 1hr postexercise to measure gut integrity and the permeability biomarker concentration for intestinal fatty-acid-binding protein, lipopolysaccharide, and lipopolysaccharide-binding protein. The runners self-reported gut symptoms 1hr postexercise and 3days postexercise. The heat condition induced large (45-370%) increases in intestinal fatty-acid-binding protein, lipopolysaccharide-binding protein, and lipopolysaccharide concentrations compared with the baseline, but induced mild gastrointestinal symptoms. Carbohydrate and polyunsaturated fat intake 24hr preexercise were associated with less lipopolysaccharide translocation. Protein, carbohydrate, total fat, and polyunsaturated fat intake (8 days) were positively associated with the percentage increase of intestinal fatty-acid-binding protein in both conditions (range of correlations, 95% confidence interval = .62-.93 [.02, .98]). Typical nutrition intake partly explained increases in biomarkers and the attenuation of symptoms induced by moderate- and high-intensity exercise under both heat and thermoneutral conditions.

Running in circles: Describing running kinematics using Fourier series

We explore the use of Fourier series to describe the kinematics of human running. From a database of 285 trials of treadmill running, we drive a musculoskeletal model with 104 anatomical joint angles to obtain kinematics. Using FFT analysis, we determine a fundamental frequency for all independent joint angles and compute average step kinematics. Finally, we represent the average step kinematics using Fourier series with numbers of coefficient pairs ranging from one through ten. We find that five or fewer Fourier coefficient pairs provide an accurate (Pearson’s correlation > 0.99 and root mean square difference < 0.5 degrees) representation for most joint angles. In conclusion, Fourier series appear to provide a compact and valid representation of running kinematics, thus enabling researchers to confidently use Fourier series in research of human running.

Hepcidin and interleukin-6 responses to endurance exercise over the menstrual cycle

The aim of the current study was to investigate iron metabolism in endurance trained women through the interleukin-6, hepcidin and iron responses to exercise along different endogenous hormonal states. Fifteen women performed 40 min treadmill running trials at 75% vVO2peak during three specific phases of the menstrual cycle: early follicular phase (day 3 ± 0.85), mid-follicular phase (day 8 ± 1.09) and luteal phase (day 21 ± 1.87). Venous blood samples were taken pre-, 0 h post- and 3 h post-exercise. Interleukin-6 reported a significant interaction for menstrual cycle phase and time (p=0.014), showing higher interleukin-6 levels at 3 h post-exercise during luteal phase compared to the early follicular phase (p=0.004) and the mid-follicular phase (p=0.002). Iron levels were significantly lower (p=0.009) during the early follicular phase compared to the mid-follicular phase. However, hepcidin levels were not different across menstrual cycle phases (p>0.05). The time-course for hepcidin and interleukin-6 responses to exercise was different from the literature, since hepcidin peak levels occurred at 0 h post-exercise, whereas the highest interleukin-6 levels occurred at 3 h post-exercise. We concluded that menstrual cycle phases may alter interleukin-6 production causing a higher inflammation when progesterone levels are elevated (days 19–21). Moreover, during the early follicular phase a significant reduction of iron levels is observed potentially due to a loss of haemoglobin through menses. According to our results, high intensity exercises should be carefully monitored in these phases in order not to further compromise iron stores.

High-intensity downhill running exacerbates heart rate and muscular fatigue in trail runners

ABSTRACT This study explores the cardiorespiratory and muscular fatigue responses to downhill (DR) vs uphill running (UR) at similar running speed or similar oxygen uptake (⩒O2). Eight well-trained, male, trail runners completed a maximal level incremental test and three 15-min treadmill running trials at ±15% slope: i) DR at ~6 km·h−1 and ~19% ⩒O2max (LDR); ii) UR at ~6 km·h−1 and ~70% ⩒O2max (HUR); iii) DR at ~19 km·h−1 and ~70% ⩒O2max (HDR). Cardiorespiratory responses and spatiotemporal gait parameters were measured continuously. Maximal isometric torque was assessed before and after each trial for hip and knee extensors and plantar flexor muscles. At similar speed (~6 km·h−1), cardiorespiratory responses were attenuated in LDR vs HUR with altered running kinematics (all p < 0.05). At similar ⩒O2 (~3 l·min−1), heart rate, pulmonary ventilation and breathing frequency were exacerbated in HDR vs HUR (p < 0.01), with reduced torque in knee (−15%) and hip (−11%) extensors and altered spatiotemporal gait parameters (all p < 0.01). Despite submaximal metabolic intensity (70% ⩒O2max), heart rate and respiratory frequency reached maximal values in HDR. These results further our understanding of the particular cardiorespiratory and muscular fatigue responses to DR and provide the bases for future DR training programs for trail runners.

Time-course of running treadmill adaptation in novice treadmill runners

ABSTRACT Studies on running biomechanics and energetics are usually conducted on a treadmill. To ensure that locomotion on a treadmill is comparable to locomotion overground, participants need to be expert in the use of the device. This study aimed to identify the number and duration of sessions needed to obtain stable measurements for spatiotemporal and metabolic parameters in unexperienced treadmill runners. Fourteen male recreational runners performed three 15-min treadmill running trials in different days at a submaximal speed. Spatiotemporal and metabolic parameters were registered at minutes: 5, 10, 15 and their within-trial and between-trial changes were analysed using a two-way repeated measures ANOVA and Bonferroni post-hoc test. Within-trial differences were found in step frequency (decreased over time), Step Length and Contact Time (increased), reaching stability at different time points. Ventilator parameters increased, reaching stability after 5–10 min, while heart rate increased progressively over time. The only between-trial differences were an increase in step length and a decrease in step frequency at min 1, between trials 1 and 3. In conclusion, at least three running trials of 15 min are required to familiarize with the device. The last 5 min of the third trial can be regarded as stable measurements.

Does enhanced footwear comfort affect oxygen consumption and running biomechanics?

Comfort as an essential parameter for running footwear is gaining importance in footwear research and development, and has also been proposed to decrease injury rate and improve metabolic demand in the paradigm of the comfort filter. The aims of this study were to determine differences in oxygen consumption and biomechanical variables associated with lower extremity injuries in response to running shoes of differing comfort. Fifteen male runners attended two testing sessions including an incremental lactate threshold test, a comfort assessment and treadmill running trials for the biomechanical and physiological measurements. Statistical analyses were performed on oxygen consumption, spatio-temporal variables including foot-ground angle and coupling angle variability of 12 couplings in five stride phases. No decrease in oxygen consumption was found in the most preferred shoe condition. Investigation of potential biomechanical contributors to changes in metabolic demands revealed differences in the stride rate between the most and least preferred condition. In coupling angle variability analyses, only one coupling (ankle dorsiflexion/plantarflexion to knee varus/valgus) yielded a significant difference between conditions in the phase including the touch down. Based on the findings of this study, previous suggestions regarding positive effects of enhanced footwear comfort during running cannot be supported – neither on economy nor on injury prevention perspective. However, a prospective study of lower extremity injury combined with measurements of biomechanical and physiological variables seems to be required for a definite support or contradiction of the comfort filter.

Altered Lower Extremity Joint Work Profiles During Inclined Running At Iso-efficiency Speeds

Inclined running is a common component of many runners’ training programs in the form of hill repeats. Runners are often forced to slow their running pace, iso-efficiency speed (ISO), during inclined running to maintain their metabolic effort. Though commonly used in training, little is known regarding the changes in joint kinetics associated with running on an inclined treadmill at an ISO speed. PURPOSE: To evaluate changes in lower extremity joint work when running on increasing inclines at ISO speeds. METHODS: Eleven NCAA Division I runners performed five 5-second treadmill running trials during each of three ISO speed inclined conditions: 0% incline, 4% incline, and 8% incline. ISO speed was confirmed using oxygen consumption (VO2) using indirect calorimetry. Kinematics and ground reaction forces were recorded simultaneously using an 8-camera motion capture system (100 Hz, Qualisys Inc.) and instrumented treadmill (1000 Hz, Bertec), respectively. Visual 3D was used to calculate ankle, knee and hip joint powers while custom software (MATLAB, MathWorks) calculated positive and negative joint work as joint power integrated with time. A repeated measures ANOVA with Tukey’s post-hoc was used to determine the effect of treadmill incline on joint work. RESULTS: Negative ankle joint work increased while negative knee and hip joint work decreased with increasing treadmill incline (Table 1). Positive ankle and hip joint work increased while positive knee work decreased with increasing treadmill incline (Table 1). CONCLUSIONS: Our findings suggest that even at ISO speeds (i.e., reduced speeds to maintain effort), inclined treadmill running increases eccentric demands on plantarflexors, and concentric demands on knee and hip extensors. These data may support altered training prescriptions for athletes recovering from joint-specific muscular injuries to minimize training-related stresses placed on those tissues.

Initial contact and toe off event identification for rearfoot and non-rearfoot strike pattern treadmill running at different speeds

The purpose of this study was to determine the validity of kinematic based initial contact (IC) and toe-off (TO) identification algorithms for rearfoot and non-rearfoot runners across a broad range of treadmill running speeds. 14 healthy active participants completed six 20–60 s treadmill running trials at 6 speeds: 2.24, 2.68, 3.13, 3.58, 4.02, and 4.48 ms−1. 3D kinematic data were collected for the last 20 s of each trial. Force plates (FP) were used as the gold standard to determine ICFP and TOFP for each step. Three algorithms for finding IC, ICMilner, ICAlvim, ICAlvim-mod, and one algorithm for finding toe off, TOFellin, were chosen for analysis. Root mean square errors (RMSE) and difference scores with 95% confidence intervals were computed for IC, TO and stance time (ST). ICAlvim RMSE ranged from 0.175 to 0.219 s. STAlvim RMSE ranged from 0.168 to 0.216 s. ICAlvim-mod RMSE ranged from 0.105 to 0.131 s. STAlvim-mod RMSE ranged from 0.108 to 0.129 s. ICMilner RMSE ranged 0.012 to 0.015 s. STMilner RMSE ranged 0.019 to 0.024 s. ICMilner accuracy was inversely related to speed. ICMilner corrected with a linear regression equation reduced differences to- 0.006 ± 0.012 s with 86% of foot strikes identified within 20 ms and 58% with 10 ms. TOFellin RMSE ranged from 0.012 to 0.016 s. ICMilner adjusted for speed and TOFellin can be used to predict IC and TO within a broad range of treadmill running speeds (2.24–4.48 ms−1) and for rearfoot and non-rearfoot strikers.

Measuring the validity and reliability of the Apple Watch as a physical activity monitor.

This study aimed to investigate the validity and reliability of the energy expenditure (EE) estimation of Apple Watch® among college students. Thirty college students completed two sets of three 10-minute treadmill walking and running trials while wearing three Apple watches and being connected to indirect calorimetry. The walking trials were at speeds of 54, 80, and 107 m·min-1 while the running trials were at 134, 161, 188 m·min-1. Energy expenditure comparisons were made using Two-way ANOVA with repeated measures. Reliability was analyzed by Intraclass Correlation. There was no significant device x speed interactions (F (15, 696)=1.113, P=0.341) between the indirect calorimetry (criterion) and Apple Watch®. The lowest Inter-Class Correlation (ICC) scores were 0.49 (95%CI) at 54 while the highest were 0.72 (95%CI) at 107 and 134 m·min-1. Apple Watch® demonstrated a low to moderate validity and reliability on measuring EE.

Potential Relationship between Passive Plantar Flexor Stiffness and Running Performance.

The present study aimed to determine the relationship between passive stiffness of the plantar flexors and running performance in endurance runners. Forty-eight well-trained male endurance runners and 24 untrained male control subjects participated in this study. Plantar flexor stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. Of the endurance runners included in the present study, running economy in 28 endurance runners was evaluated by measuring energy cost during three 4-min trials (14, 16, and 18 km/h) of submaximal treadmill running. Passive stiffness of the plantar flexors was significantly higher in endurance runners than in untrained subjects. Moreover, passive plantar flexor stiffness in endurance runners was significantly correlated with a personal best 5000-m race time. Furthermore, passive plantar flexor stiffness in endurance runners was significantly correlated with energy cost during submaximal running at 16 km/h and 18 km/h, and a trend towards such significance was observed at 14 km/h. The present findings suggest that stiffer plantar flexors may help achieve better running performance, with greater running economy, in endurance runners. Therefore, in the clinical setting, passive stiffness of the plantar flexors may be a potential parameter for assessing running performance.