Are Men Cheaper Than Women? Insights From Walking Economy

ARE MEN CHEAPER THAN WOMEN? INSIGHTS FROM WALKING ECONOMY Nicole S. Schultz and Peter G. Weyand Southern Methodist University, Locomotor Performance Laboratory, Department of Applied Physiology and Wellness, Dallas, TX 75205 Introduction: The metabolic energy cost of human walking has been extensively studied. However, whether men and women require the same amount of energy (per kg of body mass) to walk at the same speed or cover the same distance remains unresolved. While most predictive algorithms incorporate only body mass and walking speed, we have recently found that mass-specific walking metabolic rates are inversely related to stature. Objective: We tested the specific hypothesis that walking economy does not differ between males and females when stature is controlled. We evaluated our hypothesis by comparing stature-matched adult males vs. females in each of three categories: short, medium and tall, at their respective most economical walking speeds. We predicted that minimum transport costs (COTmin, ml O2·kg-1·m-1) would not vary between gender groups of each stature. Methods: 30 subjects (15 male, 15 female) walked on a level treadmill at speeds ranging from 0.4 m·s-1 to 1.9 m·s-1. Indirect calorimetry was used to measure rates of oxygen uptake under steady-state conditions (Parvo Medics TrueOne 2400, Sandy, UT). Analysis: Minimum net transport cost, or net transport cost at the most economical walking speed, was determined for each subject by: 1) subtracting resting rates of oxygen uptake from the gross rates measured (VO2net, ml O2·kg-1·min-1), and 2) dividing VO2net by walking speed to identify the minimum COT. Unpaired t-tests were used to compare males and females within each stature group. Results: Transport costs were essentially identical for male and female groups of all three statures: short, medium and tall, and were inversely related to stature as expected. Conclusion: We conclude that men and women are equally cheap and gender does not influence walking energy expenditure. The mass-specific energy cost of transport does not differ in males and females of the same stature

UPPER EXTREMITY MOTION AND SPRINT RUNNING: A FAREWELL TO ARMS?

Despite a lack of prior research on the topic, the sport coaching community has popularized the use of arm drills for athletes with the intent to enhance sprinting performance. The purpose of this study was to identify the effect of self-restricted arm motion on sprint running velocity. Track & field athletes and team sport athletes (n=15) completed 12 30-meter sprints (six with normal arm motion, six with restricted arm motion) while radar data was collected to quantify running velocity. Using a mono-exponential function, velocity profiles were created for each trial which produced four outcome variables: vmax, amax, τ, and 30-meter sprint time. Differences in group means for all four outcome variables were not substantial between the two experimental conditions. It was concluded that the use of arm motion during maximal effort sprinting does not play a major role in running velocity enhancement

Human Sprint Running Mechanics: Do Right and Left Legs Apply Equal Ground Forces?

Introduction: A growing body of research has focused on between-leg asymmetry as a critical factor for athletic performance and dysfunction. Specifically, various measures of between-leg asymmetry during running have been investigated in both healthy and injured populations. However, while the most important factor for running performance is the magnitude and rate of ground force application, it is not known whether the right and left legs typically apply equal ground forces at faster running speeds. Objective: In a healthy population of athletic female participants, we aimed to: 1) compare the mechanics of ground force application between right and left legs during moderate and top speed running, and 2) evaluate if the right vs. left leg asymmetries observed at intermediate speeds are more pronounced at faster speeds. Hypothesis: We hypothesized that the forces applied by the right and left legs of healthy athletes would agree to within 10% or less at both moderate and top speed. Participants: Nine female intercollegiate soccer players volunteered for the study (age: 19.4 ± 1.0 years, height: 1.72 ± 0.04 m, mass: 69.0 ± 7.2 kg). Data Collection: Ground force data was acquired at 1,000 Hz using a custom high-speed, three-axis force treadmill (AMTI, Watertown, MA). Data was analyzed for trials at 5.0 m•s-1 and each individual’s top speed. Top speed was defined as the fastest speed where the participant could complete eight consecutive steps on the treadmill without drifting backward more than 0.2 m. Outcome Measures: Ground contact time, vertical force, and vertical impulse were analyzed. Vertical force was normalized to body weight (Wb) and vertical impulse was calculated in body weight • seconds (Wb•s). For all trials, these variables were averaged for right vs. left footfalls, and percentage difference was calculated to quantify between-leg asymmetry. Results: Top speeds ranged from 7.21 to 8.26 m•s-1 (7.83 ± 0.38 m•s-1). At 5.0 m•s-1, the mean between-leg asymmetry was 2.3 ± 1.2 % for ground contact time, 1.9 ± 1.3 % for vertical force, and 2.3 ± 1.9 % for vertical impulse. At top speed, the mean between-leg asymmetry was 3.5 ± 2.8 % for ground contact time, 5.5 ± 3.0 % for vertical force, and 8.3 ± 4.8 % for vertical impulse. Conclusions: We conclude that the right and left legs apply ground force similarly during moderate and top-speed sprint running in healthy female athletes

A general relationship links gait mechanics and running ground reaction forces

The relationship between gait mechanics and running ground reaction forces is widely regarded as complex. This viewpoint has evolved primarily via efforts to explain the rising edge of vertical force– time waveforms observed during slow human running. Existing theoretical models do provide good rising-edge fits, but require more than a dozen input variables to sum the force contributions of four or more vague components of the body’s total mass (mb). Here, we hypothesized that the force contributions of two discrete body mass components are sufficient to account for vertical ground reaction force– time waveform patterns in full (stance foot and shank, m1=0.08mb; remaining mass, m2=0.92mb). We tested this hypothesis directly by acquiring simultaneous limb motion and ground reaction force data across a broad range of running speeds (3.0–11.1 m s−1 ) from 42 subjects who differed in body mass (range: 43–105 kg) and foot-strike mechanics. Predicted waveforms were generated from our two-mass model using body mass and three stride-specific measures: contact time, aerial time and lower limb vertical acceleration during impact. Measured waveforms (N=500) differed in shape and varied by more than twofold in amplitude and duration. Nonetheless, the overall agreement between the 500 measured waveforms and those generated independently by the model approached unity (R2 =0.95 ±0.04, mean±s.d.), with minimal variation across the slow, medium and fast running speeds tested (ΔR2 ≤0.04), and between rear-foot (R2 =0.94±0.04, N=177) versus fore-foot (R2 =0.95±0.04, N=323) strike mechanics. We conclude that the motion of two anatomically discrete components of the body’s mass is sufficient to explain the vertical ground reaction force–time waveform patterns observed during human running

Running impact forces: from half a leg to holistic understanding – comment on Nigg et al.

Running impact forces have immediate relevance for the muscle tuning paradigm proposed here and broader relevance for overuse injuries, shoe design and running performance. Here, we consider their mechanical basis. Several studies demonstrate that the vertical ground reaction force-time (vGRFT) impulse, from touchdown to toe-off, corresponds to the instantaneous accelerations of the body’s entire mass (Mb) divided into two or more portions. The simplest, a two-mass partitioning of the body (lower-limb, M1=0.08•Mb; remaining mass, M2=0.92•Mb) can account for the full vGRFT waveform under virtually all constant-speed, level-running conditions. Model validation data indicate that: 1) the non-contacting mass, M2, often accounts for one-third or more of the early “impact” portion of the vGRFT, and 2) extracting a valid impact impulse from measured force waveforms requires only lower-limb motion data and the fixed body mass fraction of 0.08 for M1

Do Horizontal Forces Matter For Horizontal Running?

DO HORIZONTAL FORCES MATTER FOR HORIZONTAL RUNNING? Kenneth P. Clark, Laurence J. Ryan, and Peter G. Weyand Southern Methodist University, Locomotor Performance Laboratory, Department of Applied Physiology and Wellness, Dallas, TX 75206 Classification of First Author: Doctoral Student Introduction: The application of ground force is widely recognized as the critical determinant of running speed. At maximal speeds, 90-98% of the total force applied is directed vertically into the running surface while horizontal (fore-aft) contributions are relatively small. Despite their small magnitude, horizontal forces are clearly essential for balance and may be important for other reasons. However, the pattern of horizontal force application across faster speeds is not well understood. Objective: For moderate to top speeds, we aimed to determine whether: 1) the horizontal forces required increase substantially, and 2) horizontal forces become larger relative to vertical forces. Participants: Two male and three female athletes volunteered for the study (age: 19.0 ± 0.6 years, height: 1.75 ± 0.06 m, mass: 71.0 ± 8.2 kg). Data Collection: Trials were completed on a high-speed, three-axis force treadmill (AMTI, Watertown, MA), with ground force data acquired at 1,000 Hz. Data was analyzed from each individual’s top speed and submaximal trials at 5.0 and 7.0 m/s. Top speed was determined by the fastest speed where the participant could complete eight steps without drifting backward 0.2 m. Outcome Measures: Because center of mass motion is determined by the mass-specific force applied and the time of force application, (i.e. impulse, or product of average force and time of application, or area under the force-time curve), we analyzed both average vertical and horizontal forces and impulses for every step. Average horizontal forces and impulses were calculated as the absolute value for the braking and propulsive phases of the horizontal force-time curve. Forces were standardized to body weight (Wb) and impulses calculated in body weight • seconds (Wb•s). The ratio of average vertical impulse to average horizontal impulse was calculated for each runner across speeds. Results: From 5.0 m/s to top speed, mean vertical and horizontal forces increased from 1.70 to 1.99 Wb and 0.29 to 0.34 Wb, respectively, and mean vertical and horizontal impulses decreased from 0.30 to 0.24 Wb•s and 0.05 to 0.04 Wb•s, respectively. From 5.0 m/s to top speed, the ratio of vertical to horizontal impulses varied by only 5.2% on average over a 1.5 to 2.0-fold range of speeds for the individuals tested and did so without consistent direction. Conclusions: The average horizontal forces and the ratio of vertical to horizontal impulses did not vary appreciably across a range of faster running speeds in a small sample of athletic subjects

High on grass? Influence of terrain on human walking economy.

Introduction: The metabolic energy cost of human walking has been extensively studied. However, the influence of terrain on the metabolic costs incurred across commonly encountered surfaces is not well understood. Objective: Our objective was to test whether the metabolic cost of walking would vary between treadmill, asphalt, and grass surfaces. We hypothesized that the metabolic energy cost of walking would not differ between the three common level walking conditions: (standard) commercial treadmill, firm asphalt and well-groomed grass field. Methods: Five subjects walked on a level treadmill at speeds ranging from 0.4 m·s-1 to 1.9 m·s-1. Indirect calorimetry was used to measure rates of oxygen uptake under steady-state conditions (Parvo Medics TrueOne 2400, Sandy, UT). The same five subjects walked at 1.0, 1.3, and 1.6 m·s-1 on a 50 meter oval course set up both in a parking lot and in a well-maintained field with short grass. Expired air was collected in Douglas bags during steady-state conditions at each of the three speeds and the gas composition (Parvo Medics TrueOne 2400, Sandy, UT) and gas volume (Dry Gas Meter, Harvard Apparatus, Holliston, MA) were measured for each bag. Analysis: Oxygen uptake was calculated based on gas analysis and volume measurements for the asphalt and grass walking tests, and was obtained from the Parvo Medics system for the treadmill tests. The relative oxygen uptake (ml·kg-1·min-1) at 1.0, 1.3, and 1.6 m·s-1 was compared across the treadmill, asphalt, and grass walking conditions. Results: Oxygen uptake was similar between treadmill and asphalt walking across all speeds; however, oxygen uptake was greater when walking on grass (14.1 ± 0.7 ml·kg-1·min-1) than on the treadmill (13.5 ± 0.6 ml·kg-1·min-1) or on asphalt (13.2 ± 0.6 ml·kg-1·min-1) by 5.2% and 6.6%, respectively. Further, the difference between walking on grass and walking on the treadmill or on asphalt was more pronounced at faster speeds. Conclusion: We conclude that the metabolic energy cost of walking on well-groomed level grass is greater than either walking on a treadmill or on asphalt

Synchronizing Cardiac Cycle Phase with Foot Strike to Optimize Cardiac Performance in Patients with Chronic Systolic Heart Failure and Cardiac Resynchronization Therapy (CRT)

Despite advances in medical and Cardiac Resynchronization Therapy (CRT), patients with chronic systolic heart failure (HF) have persistent symptoms including dyspnea on exertion and exercise intolerance. Novel strategies to improve exercise performance in these patients, such as optimizing cardio-locomotor coupling, could be particularly beneficial to improve functional capacity. For example, runners display a lower heart rate and higher oxygen pulse, suggestive of a higher stroke volume (SV), when foot strike occurs in diastole. Whether patients with HF undergoing CRT can similarly increase SV is unknown. PURPOSE: To compare the effects of diastolic versus systolic foot strike timing on exercise hemodynamics in patients with HF and CRT. METHODS: Ten patients (Age: 58 ± 17 years, 40% Female) with HF and previously implanted CRT pacemakers completed repeated 5-minute bouts of walking on a treadmill at a fixed but individualized speed (range: 1.5-3mph). Participants were randomized to walking to an auditory tone to synchronize their foot strike to either the systolic (ECG R-wave; 0 or 100%±15% or R-R interval) or diastolic phase (45±15% of the R-R interval) of their cardiac cycle. Participants were included if ≥50% of their steps were valid (i.e. in time). Patients wore a chest strap with an attached ECG sensor and accelerometer (CounterpaceR). Foot strike timing and associated valid step counts were assessed via CounterpaceR or post-hoc analysis of foot strike waveforms. Cardiopulmonary parameters were measured breath by breath via indirect calorimetry and cardiac output was measured via acetylene rebreathing, with SV calculated as the quotient of cardiac output and heart rate. RESULTS: There was no difference in oxygen uptake between conditions (1.02 ± 0.44 vs. 1.04 ± 0.44 L/min, P=0.298). When compared to systolic walking, stepping in diastole was associated with higher SV (Diastolic: 80 ± 28 vs. Systolic: 74 ± 26 ml, P=0.003) and cardiac output (8.3 ± 3.5 vs. 7.9 ± 3.4 L/min, P=0.004); heart rate (paced) was not different between conditions (101 ± 15 vs. 103 ± 14 bpm, P=0.300). Mean arterial pressure was significantly lower during diastolic walking (85 ± 12 vs. 98 ± 20 mmHg, P=0.007). CONCLUSION: In patients with HF and previous CRT, synchronizing foot strike with diastole during walking increased SV and cardiac output and reduced arterial pressure. Our findings indicate that in such paced hearts, diastolic stepping increases oxygen delivery and decreases afterload, which may facilitate increased exercise capacity. Therefore, if added to pacemakers, this cardio-locomotor coupling technology may maximize CRT efficiency and increase exercise participation and quality of life in patients with HF

Molecular mechanism of ligand recognition by membrane transport protein, Mhp1

The hydantoin transporter Mhp1 is a sodium-coupled secondary active transport protein of the nucleobase-cation-symport family and a member of the widespread 5-helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site-directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5-substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5-substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5-(2-naphthylmethyl)-L-hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1

Sprint start kinetics of amputee and non-amputee sprinters

The purpose of this study was to explore the relationship between the forces applied to the starting blocks and the start performances (SPs) of amputee sprinters (ASs) and non-amputee sprinters (NASs). SPs of 154 male and female NASs (100-m personal records [PRs], 9.58–14.00 s) and 7 male ASs (3 unilateral above knee, 3 unilateral below knee, 1 bilateral below knee; 100 m PRs, 11.70–12.70 s) with running specific prostheses (RSPs) were analysed during full-effort sprint starts using instrumented starting blocks that measured the applied forces in 3D. Using the NAS dataset and a combination of factor analysis and multiple regression techniques, we explored the relationship between force characteristics and SP (quantified by normalized average horizontal block power). Start kinetics were subsequently compared between ASs and NASs who were matched based on their absolute 100 m PR and their 100 m PR relative to the world record in their starting class. In NASs, 86% of the variance in SP was shared with five latent factors on which measured parameters related to force application to the rear and front blocks and the respective push-off directions in the sagittal plane of motion were loaded. Mediolateral force application had little influence on SP. The SP of ASs was significantly reduced compared to that of NASs matched on the basis of relative 100-m PR (−33.8%; d = 2.11, p < 0.001), while a non-significant performance reduction was observed when absolute 100-m PRs were used (−17.7%; d = 0.79, p = 0.09). These results are at least partially explained by the fact that force application to the rear block was clearly impaired in the affected legs of ASs