Jeremy J. Houser

Comparison of Gait Patterns between Young and Elderly Women: An Examination of Coordination:

This study investigated intralimb coordination during walking in young and elderly women using the theoretical model of dynamical systems. 20 women, 10 Young (M age = 24.6 yr., SD = 3.2 yr.) and 10 Elderly (M age = 73.7 yr., SD = 4.9 yr.), were videotaped during free speed gait and gait perturbed by an ankle weight. Two parameters, one describing the phasing relationship between segments (mean absolute relative phase) and the other the variability of this relationship (deviation in phase), were calculated from the kinematics. Two-way analysis of variance (age and weight) with repeated measures on weight indicated that during the braking period the weight increased the mean absolute relative phase between the shank and the thigh and decreased it between the foot and the shank. The Elderly women had significant smaller values for the mean absolute relative phase between the shank and the thigh during the braking period. For the same period, deviation in phase increased for the segmental relationship between the shank and the thigh. The findings suggest that changes in intralimb coordination take place with asymmetrical weighting and the aging process. These changes are most clearly present during the braking period.

Comparison Between Hand and Electronic Timing of 40-yd Dash Performance in College Football Players

Mayhew, JL, Houser, JJ, Briney, BB, Williams, TB, Piper, FC, and Brechue, WF. Comparison between hand and electronic timing of 40-yd dash performance in college football players. J Strength Cond Res 24(2): 447-451, 2010-The purpose of this study was to determine the difference between hand and electronic timing of 40-yd dashes in college football players. National Collegiate Athletic Association Division II players (n = 59) were measured during a 40-yd sprint by electronic timing and simultaneously by 7 experienced hand timers using digital stopwatches. Electronic times were initiated by lifting the hand from a switch mat and stopped by the torso passing through an infrared beam. Hand timers initiated timing on first movement of the player from a 3-point stance. To establish performance and timing reliabilities, 32 players completed a second trial. Interrater reliability for hand timing was intraclass correlation coefficient (ICC) = 0.987 (p < 0.001). Five of the 7 timers did not differ significantly (p > 0.05) in their timing. The maximum difference among the hand timers on any given trial was 0.19 ± 0.14 seconds, with a 95% confidence interval (CI) of −0.08 to 0.41 seconds. Hand timing (4.85 ± 0.28 seconds) was significantly faster (p < 0.001) than electronic timing (5.16 ± 0.28 seconds), producing an average difference of 0.31 ± 0.07 seconds (6.0 ± 1.3%) and a 95% CI on the average difference of −0.44 to −0.18 seconds. The correlation between electronic timing and hand timing was ICC = 0.985 (p < 0.001). Practically speaking, electronic timing produces the best measurement of 40-yd dash speed, and using the hand timing produces consistently but significantly faster times.

Comparison of Speed and Agility Performance of College Football Players on Field Turf and Natural Grass

Gains, GL, Swedenhjelm, AN, Mayhew, JL, Bird, HM, and Houser, JJ. Comparison of speed and agility performance of college football players on field turf and natural grass. J Strength Cond Res 24(10): 2613-2617, 2010-The purpose of this study was to determine the difference in 40-yd dash and proagility times performed on field turf (FT) and natural grass (NG). Red-shirt freshmen National Collegiate Athletic Association Division II college football players (n = 24) performed 2 trials each of a 40-yd dash and proagility run on each surface. Sprints were timed by an electronic timing system (ET) and by 2 hand timers (HTs). Agility was timed on each surface by 2 HTs. There was no significant difference in 40-yd dash times between FT and NG using ET (FT: 5.34 ± 0.30 seconds, NG: 5.33 ± 0.33 seconds) or HT (FT: 5.06 ± 0.31 seconds, NG: 5.11 ± 0.29 seconds). Hand timer 40-yd dashes were significantly faster than ET 40-yd dashes on both surfaces, with the difference between HT and ET on FT (−0.28 ± 0.11 seconds) significantly greater than the difference on NG (−0.22 ± 0.06 seconds). The time differences between surfaces were significantly correlated (r = 0.12, p = 0.56). Proagility times were significantly faster on FT (4.49 ± 0.28 seconds) than on grass (4.64 ± 0.33 seconds). Thus, it appears that straight-ahead sprint speed is similar between FT and NG, but change-of-direction speed may be significantly faster on FT.

Voluntary neuromuscular activation is enhanced when paired with a mechanical stimulus to human plantar soles

The purpose of this investigation was to determine if the location and the timing relative to muscle activation onset, of a mechanical stimulus applied to the soles impacted the neuromuscular activation associated with a voluntary movement. The subjects completed a series of dorsiflexion or plantarflexion movements during which a stimulus was applied to either the heel or ball of the foot at one of three time periods relative to the initiation of the agonist muscle. Surface electromyography from the tibialis anterior and soleus was collected during the movements. The results show that if the stimulus was applied shortly before agonist muscle activation, regardless of stimulation site, the neuromuscular activity associated with the movement was greatly increased.

The effects of shoe traction and obstacle height on lower extremity coordination dynamics during walking

This study aims to investigate the effects of shoe traction and obstacle height on lower extremity relative phase dynamics (analysis of intralimb coordination) during walking to better understand the mechanisms employed to avoid slippage following obstacle clearance. Ten participants walked at a self-selected pace during eight conditions: four obstacle heights (0%, 10%, 20%, and 40% of limb length) while wearing two pairs of shoes (low and high traction). A coordination analysis was used and phasing relationships between lower extremity segments were examined. The results demonstrated that significant behavioral changes were elicited under varied obstacle heights and frictional conditions. Both decreasing shoe traction and increasing obstacle height resulted in a more in-phase relationship between the interacting lower limb segments. The higher the obstacle and the lower the shoe traction, the more unstable the system became. These changes in phasing relationship and variability are indicators of alterations in coordinative behavior, which if pushed further may have lead to falling.

Effect of competitiveness on forty-yard dash performance in college men and women.

The objective of this study was to determine performance differences between individual and competitive trials of the 40-yard dash. Physically active college men (n = 25) and women (n = 29) performed an individual 40-yard dash, followed by completion of the Sports Competition Trait Inventory (SCTI) before performing a paired 40-yard dash against a time-matched competitor. All sprints were performed on an indoor rubberized track using photoelectric gates to start and stop a digital timer. In addition, 3 timers used hand-held stopwatches to record the individual sprint time. There was no significant difference (p < 0.10) between men (120.3 ± 16.6) and women (111.7 ± 20.3) on the SCTI. There was no significant difference between individual and competitive 40-yard dash times for either men (5.21 ± 0.24 and 5.19 ± 0.23 seconds, respectively) or women (6.12 ± 0.31 and 6.11 ± 0.32 seconds, respectively). The correlation between SCTI and both individual and competitive 40-yard dashes was significant (p < 0.05) for women (r = −0.45 and = 0.44, respectively) but not for men (r = −0.10 and 0.10, respectively). Electronic times (5.70 ± 0.54 seconds) were not significantly different from 1 hand-timer (5.71 ± 0.56 seconds) but were significantly faster than the other 2 timers (5.80 ± 0.58 and 5.82 ± 0.57 seconds). Averaging the 3 hand times (5.78 ± 0.56 seconds) for comparison with the electronic timing (5.70 ± 0.54 seconds) produced a high correlation (r = 0.96) but a significantly slower time (p < 0.05). A competitive environment does not appear to improve short sprint times in either men or women. In addition, hand timing may not always produce faster times compared to electronic timing.

Foot strike patterns after obstacle clearance during running

PURPOSE Running over obstacles of sufficient height requires heel strike (HS) runners to make a transition in landing strategy to a forefoot (FF) strike, resulting in similar ground reaction force patterns to those observed while landing from a jump. Identification of the biomechanical variables that distinguish between the landing strategies may offer some insight into the reasons that the transition occurs. The purpose of this study was to investigate the difference in foot strike patterns and kinetic parameters of heel strike runners between level running and running over obstacles of various heights. METHODS Ten heel strike subjects ran at their self-selected pace under seven different conditions: unperturbed running (no obstacle) and over obstacles of six different heights (10%, 12.5%, 15%, 17.5%, 20%, and 22.5% of their standing height). The obstacle was placed directly before a Kistler force platform. Repeated measures ANOVAs were performed on the subject means of selected kinetic parameters. RESULTS The statistical analysis revealed significant differences (P < 0.004) for all of the parameters analyzed. The evaluation of the center of pressure and the ground reaction forces indicated that the foot strike patterns were affected by the increased obstacle height. Between the 12.5% and 15% obstacle conditions, the group response changed from a heel strike to a forefoot strike pattern. CONCLUSIONS At height > 15%, the pattern was more closely related to the foot strike patterns found in jumping activities. This strategy change may represent a gait transition effected as a mechanism to protect against increased impact forces. Greater involvement of the ankle and the calf muscles could have assisted in attenuating the increased impact forces while maintaining speed after clearing the obstacle.

Stepping over obstacles of different heights and varied shoe traction alter the kinetic strategies of the leading limb

This study aims to investigate the effects of shoe traction and obstacle height on friction during walking to better understand the mechanisms required to avoid slippage following obstacle clearance. Ten male subjects walked at a self-selected pace during eight different conditions: four obstacle heights (0%, 10%, 20% and 40% of limb length) while wearing two different pairs of shoes (low and high traction). Frictional forces were calculated from the ground reaction forces following obstacle clearance, which were sampled with a Kistler platform at 960 Hz. All frictional peaks increased with increases in obstacle height. Low traction shoes yielded smaller peaks than high traction shoes. The transition from braking to propulsion occurred sooner due to altered control strategies with increased obstacle height. Collectively, these results provided insights into kinetic strategies of leading limb when confronted with low traction and high obstacle environments. This study provides valuable information into the adaptations used to reduce the potential of slips/falls when confronted with environments characterised by low shoe–floor friction and obstacles. It also provides the necessary foundation to explore the combined effects of shoe traction and obstacle clearance in elderly people, more sensitive to slippage.