Smokeless tobacco, reaction time, and strength in athletes.

PURPOSE: This study investigated the effects of smokeless tobacco on reaction time and strength in a group of Division III athletes. METHODS: Athletes were tested for simple and choice reaction time, maximum voluntary force, and maximum rate of force generation of the knee extensors on a KinCom dynamometer at 250 degrees.s-1. Smokeless tobacco-using athletes (N = 20) were tested while both using and after abstaining from smokeless tobacco. Another group of athletes (N = 20) who did not use smokeless tobacco served as a control group. RESULTS: Simple and complex reaction times were not affected by smokeless tobacco use or abstention. In the simple reaction time test, maximum voluntary knee extensor force was higher in the smokeless tobacco-using group while abstaining (P < 0.05). Maximum rate of force generation in the simple reaction time test was not statistically different between the conditions. In the choice reaction test, both strength parameters (maximum force and maximum rate of force generation) were higher in the user group while abstaining (P < 0.05) compared with the using condition. The strength parameter measurements in the control group were not statistically different from the tobacco-using group, while either using or abstaining. CONCLUSIONS: We conclude that smokeless tobacco use has no effect on reaction time but may detrimentally influence maximum voluntary force and maximum rate of force generation.

On the assumption of bilateral lower extremity joint moment symmetry during the sit-to-stand task.

This study examined the validity of the assumption of bilateral lower extremity joint moment symmetry during the sit-to-stand motion for a group of young (n = 7) and a group of elderly (n = 7) female subjects. Two force plates and a motion analysis system were used to determine peak joint moments at the ankles, knees, and hips following liftoff from a chair. Statistically, bilateral asymmetries in peak joint moments were found at the knee joint in the young group [a right to left difference of 0.43% BW x BH (body weight x body height)] and at the hip joint in both subject groups (differences of 0.20% BW x BH and 1.09% BW x BH for the young and elderly subjects, respectively). Subsequent data analysis, using an algorithm that assumed bilateral ground reaction force (GRF) symmetry, was performed to determine whether the bilateral differences were a result of kinematic or GRF asymmetry. It was concluded from these results that both the kinematic and GRF data account for the bilateral asymmetry. The results of the subsequent analysis also showed that the method which assumed bilateral GRF symmetry underestimated the peak joint moments at the ankles, knees, and hips, with the greatest difference between methods being 0.10% BW x BH for the ankle joint. The results of this study suggest that the assumption of bilateral symmetry of lower extremity joint moments during the sit-to-stand is not valid. However, the biomechanical significance of the errors associated with assuming symmetry must also be taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)

Visual guidance to force plates does not influence ground reaction force variability.

Gait analysis methods commonly require the subject to avoid visual guidance, that is, targeting, the force plate upon which a foot-strike is necessary. The putative rationale underlying the preference for not using targeting is the unsubstantiated contention that gait is altered. This study evaluated the influence of force plate targeting on the variability of ground reaction forces (GRF) in 15 normal subjects. Secondary factors of single vs multiple steps to the force plate and whether or not subjects were informed of the study's primary purpose were also examined. ANOVA main effects revealed that targeting did not significantly affect GRF variability (p > 0.05). A significant main effect of the number of steps required to reach the force plate on AP force variability was found (p = 0.002). Prior knowledge of the purpose of the study did not significantly affect GRF variability (p > 0.05). It was concluded that the variability of ground reaction forces is not significantly affected by targeting the force plate. Thus, targeting would not be expected to influence the variability of calculated kinetic variables that are subservient to GRF.

Converting Chattecx Balance System vertical reaction force measurements to center of pressure excursion measurements.

BACKGROUND AND PURPOSE: The purpose of this study was to determine the precision with which the postural stability data generated by the Chattecx Balance System could be converted to center of pressure displacement measurements. SUBJECTS: Two men and one woman were selected to represent a broad range of body sizes (age = 23-33 years, height = 154-175 cm, weight = 45-80 kg). METHODS: The Balance System load cells were placed on a force plate, and data were collected simultaneously from the Balance System and the force plate while the subjects performed standardized postural tasks. Linear regression analysis was used to characterize the relationship between the estimated center of pressure from the Balance System and the calculated center of pressure from the force plate. RESULTS: Significant linear relationships between the center of pressure estimated from the Balance System and the center of pressure calculated from the force plate were determined (all R2 values = > .90). CONCLUSION AND DISCUSSION: System data can be converted, and the methods recommended for use with the Balance System are described.

Effects of prophylactic ankle supports on pronation during gait.

We performed a gait analysis of 12 healthy subjects in order to analyse the rear foot pronation-supination angle and the shift of centre of pressure (COP) during walking. We used a video system and a force plate and examined the effects of semi-rigid Air-Stirrup brace, lace-up cloth RocketSoc brace, ankle taping and no bracing. Both the lace-up cloth brace and taping increased the maximum pronation angle during the stance phase. The lace-up cloth brace alone was associated with a larger maximum pronation velocity. With the lace-up cloth brace and taping, the COP was more laterally placed, allowing greater leverage about the subtalar axis and thus increasing the tendency toward pronation. The two braces and the tape did not similarly affect ankle joint biomechanics during gait. The ability to reduce excessive amounts of pronation is an important design consideration for prophylactic ankle supports.

Kinematics of recovery from a stumble.

BACKGROUND: Injuries most frequently related to accidents in elderly persons are falls during locomotion and stair ascent and descent. Although numerous risk factors have been related to falling behavior, effective strategies to predict and prevent falls have not evolved. The rationale underlying this study was that systematic experimental and analytical investigation of the effects of perturbations during locomotion and the subsequent requisites for recovery could lead to the development of clinically relevant evaluation(s) capable of identifying a predisposition to falling. The present study is the first biomechanical investigation of recovery from an anteriorly directed stumble. METHODS: Seven healthy, young males participated in this study. While the subjects walked along a walkway in the laboratory, stumbles were unexpectedly induced using a mechanical obstacle. Videotape records of these trials were analyzed and selected sagittal plane kinematics extracted. RESULTS: The perturbation caused an increase in the maximum trunk flexion angle from 4.3 degrees (control) to 18.3 degrees (p = .057), and this change was significantly associated with preperturbation walking velocity (p = .036). The maximum hip and knee flexion angles increased from 26 to 47 degrees (p = .039) and from 60 to 89 degrees (p = .009), respectively. The increases in maximum hip flexion velocity (79%) and maximum knee extension velocity (36%) were not significant. CONCLUSIONS: Identification of the principal elements of control during perturbed locomotion can contribute to understanding the relationship between specific age-related performance deficits and some types of falling behavior. The results suggest that recovery from a stumble is dependent upon lower extremity muscular power and the ability to restore control of the flexing trunk.