Jeff A. Nessler

Interpersonal synchronization during side by side treadmill walking is influenced by leg length differential and altered sensory feedback

UNLABELLED Unintentional synchronization of stepping occurs frequently between two people walking side by side, yet little is known regarding the neurological and biomechanical mechanisms that underlie this coupling. The purpose of this study was to quantify the relationship between leg length differential, select variables related to sensory feedback, and unintentional, interpersonal synchronization during gait. METHODS Twenty pairs of participants stepped on side by side treadmills under six different conditions in which visual, auditory, and tactile feedback were altered. RESULTS When compared with an estimate of synchronization expected to occur by chance, synchronization of stepping was significantly greater in each sensory condition examined. Overall, 62% of pairs exhibited unintentional step frequency locking. Pairs that exhibited entrainment had significantly lower leg length differences between partners (independent t-test, p=.044), and a significant relationship was found between leg length difference and both difference in frequency of stepping (R(2)=.258, p<.022) and frequency locking (R(2)=0.307, p=.011). Altering sensory information appeared to have little effect on the amount of step frequency locking, but improved phase angle locking. Specifically, the addition of a mechanical coupling between participants resulted in a significant increase in the amount of time spent phase locked when compared with the case where normal vision and sound were restricted between participants. DISCUSSION These data suggest that unintentional gait entrainment can be reproduced in a laboratory setting using side by side treadmills, and that anthropometric properties, such as leg length, have a significant effect on gait synchronization. Further, alterations in sensory information can affect unintentional, interpersonal synchronization, but this behavior appears to be relatively robust to changes in sensory feedback pathways related to gait.

Nonlinear time series analysis of knee and ankle kinematics during side by side treadmill walking

Nonlinear time series analysis was used to estimate maximal Lyapunov exponents of select ankle and knee kinematics during three different conditions of treadmill walking: independent, side by side, and side by side with forced synchronization of stepping. Stride to stride variability was significantly increased for the condition in which individuals walked side by side and synchronized unintentionally when compared to the conditions of forced synchronization and independent walking. In addition, standard deviations of three kinematic variables of lower extremity movement were significantly increased during the condition in which unintentional synchronization occurred. No relationship was found between standard deviation and estimates of maximal Lyapunov exponents. An increase in kinematic variability during side by side walking for nonimpaired individuals who are not at risk of falling suggests that variability in certain aspects of performance might be indicative of a healthy system. Modeling this variability for an impaired individual to imitate may have beneficial effects on locomotor function. These results may therefore have implications for the rehabilitation of gait in humans by suggesting that a different functional outcome might be achieved by practicing side by side walking as opposed to more commonly used strategies involving independent walking.

Kinematic analysis of side-by-side stepping with intentional and unintentional synchronization.

Interpersonal synchronization of stepping during side-by-side walking may assist in the rehabilitation of gait for mildly impaired individuals. However, little is known regarding the effects of step synchronization on lower limb movement kinematics. The purpose of this study was to compare normal treadmill walking to walking under conditions of intentional and unintentional synchronization of stepping. Twenty pairs of subjects walked on side-by-side treadmills independently, paired (side-by-side under conditions in which unintentional synchronization was likely to occur), and paired with forced synchronization (instructed to purposely synchronize stepping). Of these 20 pairs, six pairs (12 individuals) demonstrated unintentional synchronization for over 99% of the paired walking trial. An optical motion capture system was used to compare lower limb kinematics for each of the three walking conditions in these six pairs. The data indicated that forced synchronization of stepping resulted in steps that were significantly smaller and faster when compared to independent and unintentional synchronization conditions. In addition, stride time standard deviation was reduced for both the intentional and unintentional synchronization conditions, but these reductions were not significant. No differences were noted between the unintentional synchronization and independent walking conditions. These results suggest that unintentional synchronization might be preferable to intentional synchronization for gait rehabilitation in certain individuals. Additional work is necessary to understand the effects of side-by-side walking and its potential for use in a therapeutic setting.

A single bout of resistance exercise does not affect nonlinear dynamics of lower extremity kinematics during treadmill walking

Peripheral fatigue has been known to result in altered force output and muscle recruitment patterns by the CNS. These changes may affect lower extremity movement during gait, and such behavior may present implications for the interpretation of nonlinear analysis of gait in situations where a subject might become fatigued. The purpose of this study was to examine the effects of a single bout of resistance training on lower extremity movement during treadmill walking in healthy subjects. Fifteen recreationally active subjects performed two 10min trials of treadmill walking at their preferred speed while knee and ankle kinematics of their right limb were recorded via optical motion capture. Between walking trials, subjects performed a series of lower extremity resistance exercises designed to induce moderate muscular fatigue. Detrended fluctuation analysis of stride length and stride time revealed that statistical persistence was unaffected by moderate muscle fatigue. Estimates of finite-time maximal Lyapunov exponents for ankle angle, knee angle, and vertical ankle movement over the short (0-1 stride) and long (4-10 strides) term were also unaffected by a single bout of resistance training. These results suggest that control of locomotion in healthy individuals, as measured by the nonlinear dynamics of lower extremity movement used here, is relatively robust to moderate muscle fatigue. Additional work with greater levels of fatigue will be necessary to fully characterize the effects of muscular fatigue on gait.

Phase resetting behavior in human gait is influenced by treadmill walking speed

Gait is often modeled as a limit cycle oscillator. When perturbed, this type of system will reset its output in a stereotypical manner, which may be shifted in time with respect to its original trajectory. In contrast to other biological oscillators, relatively little is known regarding the phase resetting properties for human gait. Because humans must often reset their gait in response to perturbation, an improved understanding of this behavior may have implications for reducing the risk of fall. The purpose of this study was to further evaluate phase resetting behaviors in human gait with particular emphasis on (1) variance of the phase resetting response among healthy individuals and (2) the sensitivity of this response to walking speed. Seventeen healthy subjects walked on a treadmill at 2.0mph, 2.5mph, and 3.0mph while their right limb was perturbed randomly every 12-20 strides. Discrete, mechanical perturbations were applied by a rope that was attached to each subjects ankle and actuated by a motorized arm. Perturbations were applied once during a select stride, always at a different point in the swing phase, and the amount of phase shift that occurred on the subsequent stride was recorded. A subset of 8 subjects also walked at their preferred walking speed for 3 additional trials on a separate day in order to provide an estimate of within-subjects variability. The results suggested that phase resetting behavior is relatively consistent among subjects, but that minor variations in phase resetting behavior are attributable to walking at different treadmill speeds.

Wearing a Wetsuit Alters Upper Extremity Motion during Simulated Surfboard Paddling.

Surfers often wear wetsuits while paddling in the ocean. This neoprene covering may be beneficial to upper extremity movement by helping to improve proprioceptive acuity, or it may be detrimental by providing increased resistance. The purpose of this study was to evaluate the effects of wearing a wetsuit on muscle activation, upper extremity motion, heart rate, and oxygen consumption during simulated surfboard paddling in the laboratory. Twelve male, recreational surfers performed two paddling trials at a constant workload on a swim bench ergometer both with and without a wetsuit. Kinematic data and EMG were acquired from the right arm via motion capture, and oxygen consumption and heart rate were recorded with a metabolic cart and heart rate monitor. Wearing a wetsuit had no significant effect on oxygen consumption or heart rate. A significant increase in EMG activation was observed for the middle deltoid but not for any of the other shoulder muscle evaluated. Finally, approximate entropy and estimates of the maximum Lyapunov exponent increased significantly for vertical trajectory of the right wrist (i.e. stroke height) when a wetsuit was worn. These results suggest that a 2mm wetsuit has little effect on the energy cost of paddling at lower workloads but does affect arm motion. These changes may be the result of enhanced proprioceptive acuity due to mechanical compression from the wetsuit.

Characterization of Activity and Cardiovascular Responses During Surfing in Recreational Male Surfers Between the Ages of 18 and 75 Years Old

Participation in surfing has evolved to include all age groups. Therefore, the purpose of this study was to determine whether activity levels and cardiovascular responses to surfing change with age. Surfing time and heart rate (HR) were measured for the total surfing session and within each activity of surfing (paddling, sitting, wave riding, and miscellaneous). Peak oxygen consumption (VO2peak) was also measured during laboratory-based simulated surfboard paddling on a modified swim bench ergometer. VO2peak decreased with age during simulated paddling (r = -.455, p < .001, n = 68). Total time surfing (p = .837) and time spent within each activity of surfing did not differ with age (n = 160). Mean HR during surfing significantly decreased with age (r = -.231, p = .004). However, surfing HR expressed as a percent of age-predicted maximum increased significantly with age. Therefore, recreational surfers across the age spectrum are achieving intensities and durations that are consistent with guidelines for cardiovascular health.

Heart Rate Responses of High School Students Participating in Surfing Physical Education.

Abstract Bravo, MM, Cummins, KM, Nessler, JA, and Newcomer, SC. Heart rate responses of high school students participating in surfing physical education. J Strength Cond Res 30(6): 1721–1726, 2016—Despite the nations rising epidemic of childhood obesity and diabetes, schools struggle to promote physical activities that help reduce risks for cardiovascular disease. Emerging data suggest that adopting novel activities into physical education (PE) curriculum may serve as an effective strategy for increasing physical activity in children. The purpose of this investigation was to characterize activity in the water and heart rates (HRs) of high school students participating in surf PE courses. Twenty-four male (n = 20) and female (n = 4) high school students (mean age = 16.7 ± 1.0 years) who were enrolled in surf PE courses at 2 high schools participated in this investigation. Daily measurements of surfing durations, average HR, and maximum HR were made on the students with HR monitors (PolarFT1) over an 8-week period. In addition, HR and activity in the water was evaluated during a single session in a subset of students (n = 11) using a HR monitor (PolarRCX5) and a video camera (Canon HD). Activity and HR were synchronized and evaluated in 5-second intervals during data analyses. The average duration that PE students participated in surfing during class was 61.7 ± 1.0 minutes. Stationary, paddling, wave riding, and miscellaneous activities comprised 42.7 ± 9.5, 36.7 ± 7.9, 2.9 ± 1.4, and 17.8 ± 11.4 percent of the surf session, respectively. The average and maximum HRs during these activities were 131.1 ± 0.9 and 177.2 ± 1.0 b·min−1, respectively. These data suggest that high school students participating in surf PE attained HRs and durations that are consistent with recommendations with cardiovascular fitness and health. In the future, PE programs should consider incorporating other action sports into their curriculum to enhance cardiovascular health.

Side by side treadmill walking reduces gait asymmetry induced by unilateral ankle weight

Asymmetric gait is a hallmark of many neurological and musculoskeletal conditions. This behavior is often the result of a decrease in the stability of interlimb coordination, and synchronization to external signals such as auditory cuing or another walking individual may be helpful for altering abnormal movement patterns. The purpose of this study was to investigate the interaction between interlimb coordination and unintentional, interpersonal synchronization of gait in healthy individuals in response to unilateral ankle loading. Fifty participants completed four trials while walking on a motorized treadmill: (1) by themselves, (2) with a partner on an adjacent treadmill, (3) by themselves with additional weight applied unilaterally to their right ankle, and (4) with both a partner and unilateral weight. As expected, the addition of unilateral weight increased asymmetry according to several spatiotemporal measures of gait, but the presence of a partner on an adjacent treadmill significantly reduced this effect. Further, the amount of unintentional, interpersonal synchronization among pairings was relatively unaffected by the addition of ankle weight to one of the partners. All pairings realized a beneficial effect on asymmetrical gait but this effect was greater for pairings that consistently synchronized unintentionally. These results suggest that side by side walking might be an effective approach for influencing bilateral coordination of gait and may hold insight for understanding gait asymmetry and interlimb movement variability.

Increasing surfboard volume reduces energy expenditure during paddling

Abstract The purpose of this study was to investigate how altering surfboard volume (BV) affects energy expenditure during paddling. Twenty surfers paddled in a swim flume on five surfboards in random order twice. All surfboards varied only in thickness and ranged in BV from 28.4 to 37.4 L. Measurements of heart rate (HR), oxygen consumption (VO2), pitch angle, roll angle and paddling cadence were measured. VO2 and HR significantly decreased on thicker boards [VO2: r = −0.984, p = 0.003; HR: r = −0.972, p = 0.006]. There was also a significant decrease in pitch and roll angles on thicker boards [Pitch: r = −0.995, p < 0.001; Roll: r = −0.911, p = 0.031]. Results from this study suggest that increasing BV reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume. Practioner Summary: This study investigated the impact of surfboard volume on energy expenditure during paddling. Results from this study suggest that increasing surfboard volume reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.