Human runners exhibit a least variable gait speed.

This study characterises the relationship between gait variability and speed in runners using data from trunk accelerations in each axis. Twelve participants of varying fitness ran on the treadmill with three sessions of six randomly ordered self-selected speeds. A VO2max test was conducted on the fourth session. Running gait was tracked with inertial sensors. The occurrence of a mid-range speed was analysed for the anterior-posterior, vertical and lateral directional coefficient of variation (CV) of root mean square (RMS) acceleration data. One participant with noisy gait signals was omitted. The results show all remaining participants consistently showed significant quadratic U-shaped relationships between vertical RMS CV acceleration and speed. Neither anterior-posterior nor lateral RMS CV acceleration were clearly related to speed. These least variable gait speeds were similar to estimates of optimal speed derived from minimum cost of transport with speed. In conclusion, there exists a mid-range speed for each runner with the least variable gait in the vertical direction, and this occurred significantly more often than would be expected by chance (P < 0.05). However, there are no prominent patterns for the anterior-posterior and lateral directions. This finding supports anecdotal evidence from runners and coaches concerning gait consistency.

Minimum cost of transport in human running is not ubiquitous.

PURPOSE: This study explores recent claims that humans exhibit minimum cost of transport (CoTmin) for running, which occurs at intermediate speed, and assesses individual physiological, gait, and training characteristics. METHODS: Twelve healthy participants with varying levels of fitness and running experience ran on a treadmill at six self-selected speeds in a discontinuous protocol over three sessions. Running speed (km·h), VO2 (mL·kg·km), CoT (kcal·km), HR (bpm), and cadence (steps per minute) were continuously measured. VO2max was measured on the fourth testing session. The occurrence of CoTmin was investigated, and its presence or absence was examined with respect to fitness, gait, and training characteristics. RESULTS: Five participants showed clear CoTmin at intermediate speed and a statistically significant (P < 0.05) quadratic CoT-speed function, whereas the other participants did not show such evidence. Participants were then categorized and compared with respect to the strength of evidence for CoTmin (ClearCoTmin and NoCoTmin). The ClearCoTmin group displayed a significantly higher correlation between speed and cadence, more endurance training and exercise sessions per week, and a marginally nonsignificant but higher aerobic capacity than the NoCoTmin group. Some runners still showed CoTmin at intermediate speed even after subtraction of resting energy expenditure. CONCLUSIONS: The findings confirm the existence of optimal speed for human running in some but not all participants. Those exhibiting COTmin undertook higher volume of running, ran with a cadence that was more consistently modulated with speed, and tended to be aerobically fitter. The ability to minimize energetic CoT seems not to be a ubiquitous feature of human running but may emerge in some individuals with extensive running experience.

Physiological tolerance times while wearing explosive ordnance disposal protective clothing in simulated environmental extremes.

Explosive ordnance disposal (EOD) technicians are required to wear protective clothing to protect themselves from the threat of overpressure, fragmentation, impact and heat. The engineering requirements to minimise these threats results in an extremely heavy and cumbersome clothing ensemble that increases the internal heat generation of the wearer, while the clothing's thermal properties reduce heat dissipation. This study aimed to evaluate the heat strain encountered wearing EOD protective clothing in simulated environmental extremes across a range of differing work intensities. Eight healthy males [age 25 ± 6 years (mean ± sd), height 180 ± 7 cm, body mass 79 ± 9 kg, VO2max 57 ± 6 ml(.) kg(-1.)min(-1)] undertook nine trials while wearing an EOD9 suit (weighing 33.4 kg). The trials involved walking on a treadmill at 2.5, 4 and 5.5 km ⋅ h(-1) at each of the following environmental conditions, 21, 30 and 37 °C wet bulb globe temperature (WBGT) in a randomised controlled crossover design. The trials were ceased if the participants' core temperature reached 39 °C, if heart rate exceeded 90% of maximum, if walking time reached 60 minutes or due to fatigue/nausea. Tolerance times ranged from 10-60 minutes and were significantly reduced in the higher walking speeds and environmental conditions. In a total of 15 trials (21%) participants completed 60 minutes of walking; however, this was predominantly at the slower walking speeds in the 21 °C WBGT environment. Of the remaining 57 trials, 50 were ceased, due to attainment of 90% maximal heart rate. These near maximal heart rates resulted in moderate-high levels of physiological strain in all trials, despite core temperature only reaching 39 °C in one of the 72 trials.

Falls in Parkinson's disease: kinematic evidence for impaired head and trunk control.

Changes in stride characteristics and gait rhythmicity characterize gait in Parkinson's disease and are widely believed to contribute to falls in this population. However, few studies have examined gait in PD patients who fall. This study reports on the complexities of walking in PD patients who reported falling during a 12-month follow-up. Forty-nine patients clinically diagnosed with idiopathic PD and 34 controls had their gait assessed using three-dimensional motion analysis. Of the PD patients, 32 (65%) reported at least one fall during the follow-up compared with 17 (50%) controls. The results showed that PD patients had increased stride timing variability, reduced arm swing and walked with a more stooped posture than controls. Additionally, PD fallers took shorter strides, walked slower, spent more time in double-support, had poorer gait stability ratios and did not project their center of mass as far forward of their base of support when compared with controls. These stride changes were accompanied by a reduced range of angular motion for the hip and knee joints. Relative to walking velocity, PD fallers had increased mediolateral head motion compared with PD nonfallers and controls. Therefore, head motion could exceed "normal" limits, if patients increased their walking speed to match healthy individuals. This could be a limiting factor for improving gait in PD and emphasizes the importance of clinically assessing gait to facilitate the early identification of PD patients with a higher risk of falling.

Spontaneous pacing during overground hill running.

PURPOSE: To investigate speed regulation during overground running on undulating terrain. METHODS: After an initial laboratory session to calculate physiological thresholds, eight experienced runners completed a spontaneously paced time trial over three laps of an outdoor course involving uphill, downhill, and level sections. A portable gas analyzer, global positioning system receiver, and activity monitor were used to collect physiological, speed, and stride frequency data. RESULTS: Participants ran 23% slower on uphills and 13.8% faster on downhills compared with level sections. Speeds on level sections were significantly different for 78.4 +/- 7.0 s following an uphill and 23.6 +/- 2.2 s following a downhill. Speed changes were primarily regulated by stride length, which was 20.5% shorter uphill and 16.2% longer downhill, whereas stride frequency was relatively stable. Oxygen consumption averaged 100.4% of runner's individual ventilatory thresholds on uphills, 78.9% on downhills, and 89.3% on level sections. Approximately 89% of group-level speed was predicted using a modified gradient factor. Individuals adopted distinct pacing strategies, both across laps and as a function of gradient. CONCLUSIONS: Speed was best predicted using a weighted factor to account for prior and current gradients. Oxygen consumption (VO2) limited runner's speeds only on uphill sections and was maintained in line with individual ventilatory thresholds. Running speed showed larger individual variation on downhill sections, whereas speed on the level was systematically influenced by the preceding gradient. Runners who varied their pace more as a function of gradient showed a more consistent level of oxygen consumption. These results suggest that optimizing time on the level sections after hills offers the greatest potential to minimize overall time when running over undulating terrain.

Balance and postural skills in normal-weight and overweight prepubertal boys.

OBJECTIVE: This study investigated differences in balance and postural skills in normal-weight versus overweight prepubertal boys. METHODS: Fifty-seven 8-10-year-old boys were categorized overweight (N = 25) or normal-weight (N = 32) according to the International Obesity Task Force cut-off points for overweight in children. The Balance Master, a computerized pressure plate system, was used to objectively measure six balance skills: sit-to-stand, walk, step up/over, tandem walk (walking on a line), unilateral stance and limits of stability. In addition, three standardized field tests were employed: standing on one leg on a balance beam, walking heel-to-toe along the beam and the multiple sit-to-stand test. RESULTS: Overweight boys showed poorer performances on several items assessed on the Balance Master. Overweight boys had slower weight transfer (p < 0.05), lower rising index (p < 0.05) and greater sway velocity (p < 0.001) in the sit-to-stand test, greater step width while walking (p < 0.05) and lower speed when walking on a line (p < 0.01) compared with normal-weight counterparts. Performance on the step up/over test, the unilateral stance and the limits of stability were comparable between both groups. On the balance beam, overweight boys could not hold their balance on one leg as long (p < 0.001) and had fewer correct steps in the heel-to-toe test (p < 0.001) than normal-weight boys. Finally, overweight boys were slower in standing up and sitting down five times in the multiple sit-to-stand task (p < 0.01). CONCLUSION: This study demonstrates that when categorised by body mass index (BMI) level, overweight prepubertal boys displayed lower capacity on several static and dynamic balance and postural skills.

Assessment of speed and position during human locomotion using nondifferential GPS.

PURPOSE: To validate a nondifferential global positioning system (GPS) to measure speed, displacement, and position during human locomotion. METHODS: Three healthy participants walked and ran over straight and curved courses for 59 and 34 trials, respectively. A nondifferential GPS receiver provided speed data by Doppler shift and change in GPS position over time, which were compared with actual speeds determined by chronometry. Displacement data from the GPS were compared with a surveyed 100-m section, and static positions were collected for 1 h and compared with the known geodetic point. RESULTS: GPS speed values on the straight course were closely correlated with actual speeds (Doppler shift: r = 0.9994, P < 0.001, Delta GPS position/time: r = 0.9984, P < 0.001). Actual speed errors were lowest using the Doppler shift method (90.8% of values within +/- 0.1 m x s(-1)). Speed was slightly underestimated on a curved path, though still highly correlated with actual speed (Doppler shift: r = 0.9985, P < 0.001, Delta GPS distance/time: r = 0.9973, P < 0.001). Distance measured by GPS was 100.46 +/- 0.49 m, and 86.5% of static points were within 1.5 m of the actual geodetic point (mean error: 1.08 +/- 0.34 m, range 0.69-2.10 m). CONCLUSIONS: Nondifferential GPS demonstrated a highly accurate estimation of speed across a wide range of human locomotion velocities using only the raw signal data with a minimal decrease in accuracy around bends. This high level of resolution was matched by accurate displacement and position data. Coupled with reduced size, cost, and ease of use, this method offers a valid alternative to differential GPS in the study of overground locomotion.

Predictors of driving assessment outcome in Parkinson's disease.

This study evaluated selected clinical and functional tests as predictors of driving safety outcomes in Parkinson's disease (PD) patients. A total of 25 PD patients and 21 age-matched controls, all regular drivers, underwent neurological evaluation and assessment of cognitive, visual, and motor function and a standardized, on-road driving assessment. The capacity of the tests to predict pass/fail driving outcomes was determined by selecting a subset with the highest predictive value from each domain and then subjecting these subsets to discriminant function analysis. Accuracy, sensitivity, specificity, and positive and negative predictive values were determined. Three relatively simple tests from the larger battery predicted passes with relatively high sensitivity (PD, 72.7%; controls, 93.8%; both combined, 85.2%); and moderate specificity (PD, 64.3%; controls, 60.0%; both combined. 63.2%). These tests assessed motor performance (Purdue Pegboard test), contrast sensitivity (Pelli-Robson test), and cognitive function (verbal version of Symbol Digit Modalities test). Adding time since diagnosis for the PD group increased sensitivity to 90.9% and specificity to 71.4%. These simple tests confer more objectivity and predictive power to clinical recommendations for driving, they reflect distinct functions that are necessary for safe driving, and they may be especially useful when on-road assessments are not feasible.

Practice effects in three-dimensional sequential rapid aiming in Parkinson's disease.

One hypothesized role of the basal ganglia, based largely on findings in Parkinson's disease (PD) patients, is the control of movement sequences. We examined changes in performance with practice of a movement sequence in PD patients and age-matched controls (n = 8 per group). Subjects practiced a complex three-dimensional sequential aiming task over 2 days, completing 180 trials, with the goal to minimize response time within specified accuracy limits. The results indicated that both groups became faster in planning the movement, and both groups moved more quickly through the sequence with practice. The PD group's decrease in movement time occurred primarily within the first 45 trials, whereas the control group continued to improve through the first 150 trials. Flight time (time between targets) to a small target decreased with practice in both groups, but flight time to a large target decreased only in the control group. This finding indicates that error corrective processes are more amenable to practice than ballistic processes in people with PD. There was little evidence that either group improved their performance by planning shorter (lower) trajectories, but rather increased mean velocity. Contact time (time on target) decreased with practice in both groups, and there were no group differences. These data indicate that practice can improve performance, both in planning and in specific execution processes.

Velocity perception and proprioception.

Proprioceptive information related to position and velocity reaches conscious perception and appears to be processed simultaneously via separate perceptual channels. Determining the fidelity of velocity perception is difficult, however, because of the interaction of distance and timing information in its derivation. There is also a complex relationship between receptor discharge and kinematic variables and thresholds for detection of proprioceptive information are increased during movement. Experiments determined the discrimination thresholds for different movement velocities when i) movement distance remained constant and duration varied; ii) movement duration remained constant and distance varied; iii) movement distance and duration were randomly varied. Discrimination thresholds increased as movement velocity increased. Velocity perception was more accurate when distance and timing cues were available, particularly at higher velocities. These results indicate that all available cues are used to make judgements of movement velocity.