The Determination of Step Frequency in 3-min Incremental Step-in-Place Tests for Predicting Maximal Oxygen Uptake from Heart Rate Response in Taiwanese Adults

The maximal oxygen uptake (VO2max) prediction models established by step tests are often used for evaluating cardiorespiratory fitness (CRF). However, it is unclear which type of stepping frequency sequence is more suitable for the public to assess the CRF. Therefore, the main purpose of this study was to test the effectiveness of two 3-min incremental step-in-place (3MISP) tests (i.e., 3MISP30s and 3MISP60s) with the same total number of steps but different step-frequency sequences in predicting VO2max. In this cross-sectional study, a total of 200 healthy adults in Taiwan completed 3MISP30s and 3MISP60s tests, as well as cardiopulmonary exercise testing. The 3MISP30s and 3MISP60s models were established through multiple stepwise regression analysis by gender, age, percent body fat, and 3MISP-heart rate. The statistical analysis included Pearson’s correlations, the standard errors of estimate, the predicted residual error sum of squares, and the Bland–Altman plot to compare the measured VO2max values and those estimated. The results of the study showed that the exercise intensity of the 3MISP30s test was higher than that of the 3MISP60s test (% heart rate reserve (HRR) during 3MISP30s vs. %HRR during 3MISP60s = 81.00% vs. 76.81%, p < 0.001). Both the 3MISP30s model and the 3MISP60s model explained 64.4% of VO2max, and the standard errors of the estimates were 4.2043 and 4.2090 mL·kg−1·min−1, respectively. The cross-validation results also indicated that the measured VO2max values and those predicted by the 3MISP30s and 3MISP60s models were highly correlated (3MISP30s model: r = 0.804, 3MISP60s model: r = 0.807, both p < 0.001). There was no significant difference between the measured VO2max values and those predicted by the 3MISP30s and 3MISP60s models in the testing group (p > 0.05). The results of the study showed that when the 3MISP60s test was used, the exercise intensity was significantly reduced, but the predictive effectiveness of VO2max did not change. We concluded that the 3MISP60s test was physiologically less stressful than the 3MISP30s test, and it could be a better choice for CRF evaluation.

Relationships between Strength and Step Frequency with Fatigue Index in Repeated Sprint Ability

Force−velocity profile (FVP) and repeated-sprint ability (RSA) tests are indicators of physical capacities in most team sport players. The purpose of this study was to examine the stride kinematics during a repeated-sprint ability (RSA) test and to analyze the relationship between Bosco’s force−velocity profile (FVP) and RSA performance in elite female field hockey players. Thirteen elite-female players performed both RSA (six 30 m maximal sprints) and jumping (CMJ weighted and body weight) tests. Sprinting time fatigue indexes during a 30 m RSA test were correlated with step frequency fatigue indexes (r > 0.7; p < 0.01). CMJ50 showed a large relationship with sprint time fatigue indexes. FV50 showed a very large relationship with sprint time fatigue indexes (r > 0.7; p < 0.01), and a large relationship with the step frequency fatigue indexes (r > 0.5; p < 0.05). This study highlighted two possible ways to improve fatigue indexes in RSA, with the aim of maximizing the distances covered at high-intensities during the matches: (a) strength training and (b) focusing on step frequency during speed training.

The relationship between physical activity intensity and volume on prospective falls in older adults

The benefits of Physical Activity (PA) for older adults have been well documented relative to several physiological and neuromuscular factors, but the direct relationship of PA to fall incidence is unclear. In particular, the influence of the intensity and volume of habitual activities of daily living is poorly understood. The purpose of this study was to evaluate the influence of general PA intensity and overall volume on prospective falls in older adults. The PA of 134 participants was recorded using accelerometers (ActiGraph-GT3X+) over 7 consecutive days. Intensity was classified as light, moderate and vigorous by step frequency. The activity of all participants was graded as sedentary to low intensity, no participant exhibited activity in the vigorous category. During the following 12-months, participants maintained a daily falls diary and completed monthly phone calls to monitor fall incidence. Responses were used to categorize participants as fallers or non-fallers. Eighteen participants experienced one or more falls during the 12-month period. There was no statistical difference between fallers and non-fallers in either total step count or the percentage of time spent in sedentary or light PA. While previous reports suggest that many falls occur during light PA, our results do not suggest that greater volumes of low intensity activities alone results in greater fall incidence. However, we suggest this result may be influenced by physical stimuli participants received within the larger overall study design including a session of repeated exposure to forward loss of balance.

A portable exotendon assisting hip and knee joints reduces muscular burden during walking

Assistive devices are used to reduce human effort during locomotion with increasing success. More assistance strategies are worth exploring, so we aimed to design a lightweight biarticular device with well-chosen parameters to reduce muscle effort. Based on the experience of previous success, we designed an exotendon to assist in swing leg deceleration. Then we conducted experiments to test the performance of the exotendon with different spring stiffness during walking. With the assistance of the exotendon, peak activation of semitendinosus decreased, with the largest reduction of 12.3% achieved with the highest spring stiffness ( p = 0.004). The peak activations of other measured muscles were not significantly different ( p = 0.15–0.92). The biological hip extension and knee flexion moments likewise significantly decreased with the spring stiffness ( p < 0.01). The joint angle was altered during the assisted phases with decreased hip flexion and knee extension. Meanwhile, the step frequency and the step length were also altered, while the step width remained unaffected. Gait variability changed only in the frontal plane, exhibiting lower step width variability. We conclude that passive devices assisting hip extension and knee flexion can significantly reduce the burden on the hamstring muscles, while the kinematics is easily altered.

Simple models highlight differences in the walking biomechanics of young children and adults

Adults conserve metabolic energy during walking by minimizing the step-to-step transition work performed by the legs during double support and by utilizing spring-like mechanisms in their legs, but little is known as to whether children utilize these same mechanisms. To gain a better understanding, we studied how children (5-6 years) and adults modulate the mechanical and metabolic demands of walking at their preferred speed, across slow (75%), preferred (100%), and fast (125%) step frequencies. We quantified the 1) positive mass-specific work done by the trailing leg during step-to-step transitions and 2) the leg's spring-like behavior during single support. On average, children walked with a 36% greater net cost of transport (COT; J/kg/m) than adults (p=0.03), yet both groups increased their net COT at varying step frequencies. After scaling for speed, children generated ∼2-fold less trailing limb positive scaled mechanical work during the step-to-step transition (p=0.02). Unlike adults, children did not modulate their trailing limb positive work to meet the demands of walking at 75% and 125% of their preferred step frequency. In single support, young children operated their stance limb with much greater compliance than adults (k̂= 6.23 vs. 11.35; p=.023). Our observations suggest that the mechanics of walking in children 5-6 years are fundamentally distinct from the mechanics of walking in adults and may help to explain a child's higher net COT. These insights have implications for the design of assistive devices for children and suggest that children cannot be simply treated as scaled down versions of adults.

How Running Give Us a High Expectations to Overcome Neurological Disorders

Whether chasing down dinner, pushing a stroller up a hill or running errands for a neighbor, we can take joy in the effort. And the more physically active you are, the more rewarding these experiences become. One of the ways that regular exercise changes your brain is by increasing the density of binding sites for endocannabinoids. Spring-like leg behavior is a general feature of mammalian bouncing gaits, such as running and hopping. Although increases in step frequency at a given running speed are known to increase the stiffness of the leg spring (kleg) in non-amputees, little is known about stiffness regulation in unilateral transfemoral amputees. Thus Consequently, the unilateral transfemoral amputees attained the desired step frequency in the unaffected limb, but were unable to match the three highest step frequencies using their affected limbs

Relationship between Step Characteristics and Race Performance during 5000-m Race

This study examined the relationship between step characteristics and race time in a 5000-m race. Twenty-one male Japanese endurance runners performed a 5000-m race. Step length, step frequency, contact time, and flight time of two gait cycles (i.e., four consecutive ground contacts) were measured every 400-m by using high-speed video image. Moreover, step length was normalized to body height to minimize the effect of body size. In addition to step characteristics on each lap, the averages of all laps and the per cent change from the first half to the second half were calculated. The average step frequency and step length normalized to body height correlated significantly with the 5000-m race time (r = −0.611, r = −0.575, respectively, p < 0.05 for both). Per cent changes in contact time and step length correlated significantly with the 5000-m race time (r = 0.514, r = −0.486, respectively, p < 0.05 for both). These findings suggest that, in addition to higher step frequency and step length normalized to body height, smaller changes in step length during a given race may be an important step characteristic to achieving superior race performance in endurance runners.

Energy optimization during walking involves implicit processing

ABSTRACT Gait adaptations, in response to novel environments, devices or changes to the body, can be driven by the continuous optimization of energy expenditure. However, whether energy optimization involves implicit processing (occurring automatically and with minimal cognitive attention), explicit processing (occurring consciously with an attention-demanding strategy) or both in combination remains unclear. Here, we used a dual-task paradigm to probe the contributions of implicit and explicit processes in energy optimization during walking. To create our primary energy optimization task, we used lower-limb exoskeletons to shift people's energetically optimal step frequency to frequencies lower than normally preferred. Our secondary task, designed to draw explicit attention from the optimization task, was an auditory tone discrimination task. We found that adding this secondary task did not prevent energy optimization during walking; participants in our dual-task experiment adapted their step frequency toward the optima by an amount and at a rate similar to participants in our previous single-task experiment. We also found that performance on the tone discrimination task did not worsen when participants were adapting toward energy optima; accuracy scores and reaction times remained unchanged when the exoskeleton altered the energy optimal gaits. Survey responses suggest that dual-task participants were largely unaware of the changes they made to their gait during adaptation, whereas single-task participants were more aware of their gait changes yet did not leverage this explicit awareness to improve gait adaptation. Collectively, our results suggest that energy optimization involves implicit processing, allowing attentional resources to be directed toward other cognitive and motor objectives during walking.

Predictive Simulations of Gait with Exoskeletons that Alter Energetics

Robotic exoskeletons, designed to augment human locomotion, have the potential to restore function in those with mobility impairments and enhance it in able-bodied individuals. However, optimally controlling these devices, to work in concert with complex and diverse human users, is a challenge. Accurate model simulations of the interaction between exoskeletons and walking humans may expedite the design process and improve control. Here, we use predictive gait simulations to investigate the effect of an exoskeleton that alters the energetic consequences of walking. To validate our approach, we re-created an past experimental paradigm where robotic exoskeletons were used to shift people’s energetically optimal step frequency to frequencies higher and lower than normally preferred. To match the experimental controller, we modelled a knee-worn exoskeleton that applied resistive torques that were either proportional or inversely proportional to step frequency—decreasing or increasing the energy optimal step frequency, respectively. We were able to replicate the experiment, finding higher and lower optimal step frequencies than in natural walking under each respective condition. Our simulated resistive torques and objective landscapes resembled the measured experimental resistive torque and energy landscapes. Individual muscle energetics revealed distinct coordination strategies consistent with each exoskeleton controller condition. Predicted step frequency and energetic outcomes were best achieved by increasing the number of virtual participants (varying whole-body anthropometrics), rather than number of muscle parameter sets (varying muscle anthropometrics). In future, our approach can be used to design controllers in advance of human testing, to help identify reasonable solution spaces or tailor design to individual users.