Age-gender differences in the reaction times of ankle muscles.

AIM: Reaction times of the hip abductor were reported to be longer in elderly women than in elderly men, and this was suggested to be related to mediolateral balance performance. The aim of the present study was to investigate the effects of age and gender on the reaction performance of ankle muscles, which have predominant roles in anterioposterior balance control. METHODS: A total of 40 elderly subjects and 40 young subjects (even number of men and women) carried out a series of isometric plantarflexions and dorsiflexions, as forcefully and quickly as possible, in response to auditory stimulus. Surface electromyogram at the dorsiflexor and plantarflexor were recorded, together with foot plantar force. Premotor time, motor time and total reaction time derived from the experimental data were compared between age groups and genders by two-way anova. RESULTS: Both dorsiflexor and plantarflexor showed similar reaction performance. Premotor time increased with age with no gender difference. Motor time increased with age in women and not in men, resulting in longer motor time in elderly women than in elderly men. Total reaction time was dominated by premotor time, so that it was longer in the elderly with no gender difference. CONCLUSION: Although age-related elongation of motor time was greater in women, total reaction time was not different between the genders. This may be related to no gender difference in anterioposterior balance performance.

Analysis of lower limb bradykinesia in Parkinson's disease patients.

AIM: Bradykinesia of the lower limb is an important limiting factor of the quality of life in parkinsonian patients. This study aims to develop quantitative measures of bradykinesia and to investigate the possible dissociation of amplitude and velocity measures and their dependence on movement direction during toe-tapping. METHODS: Subjects included 39 patients with PD, as well as 14 healthy control subjects. A gyrosensor on the dorsum of a foot was used to measure ankle joint movement during toe-tapping. Four representations (root-mean square, mean peak, coefficient of variation in peaks, peak in the last 5 s) for each of amplitude and velocity and for each of plantar flexion and dorsiflexion movement of toe-tapping were investigated. Outcome measures were compared between patients and controls, and their correlations with clinical scores were investigated. Category distributions of outcome measures in patients were analyzed. RESULTS: All outcome measures were smaller in patients than in controls (P < 0.001) and correlated well with clinical scores (P < 0.01). The mean peak of plantar-flexion velocity and variation of dorsiflexion velocity best represented the clinical toe-tapping score (r = 0.72-0.81). All clinical scores showed better correlation with velocity than with amplitude, and velocity was more affected (dispersed from the performance of controls) than amplitude. Movement directions had a slight effect on the results; specifically, the magnitude measures better correlated during plantar flexion and the variation measure better correlated during dorsiflexion. CONCLUSION: The suggested measures represented clinical scores well and are expected to be helpful in clinical diagnosis of lower limb bradykinesia. Possible dissociations of amplitude and speed impairments and of movement directions in PD deserve further investigation.

Age-sex differences in the hip abductor muscle properties.

AIM: Elderly women are reported to have worse postural balance in the mediolateral direction than elderly men, which may be related to hip lateral muscle properties. The purpose of this study was to investigate the effects of sex, age and their interactions on hip abductor muscle properties. METHODS: Thirty elderly and 30 young healthy subjects were recruited in this study. Subjects were instructed to abduct their leg as forcefully and quickly as possible under isometric condition, in response to audible beeps. Electromyogram was measured on the gluteus medius muscle and abduction torque was measured. Investigated muscle properties included torque amplitudes and muscle contraction timings. Muscle contraction timings were designated as premotor time, electromechanical delay and total reaction time. The effects of sex, age and their interactions on muscle properties were analyzed. RESULTS: Women showed smaller torque amplitudes, longer electromechanical delay and longer total reaction time than men (P < 0.01), whereas no sex difference was observed in association with premotor time (P = 0.15). Age-sex interaction was significant in torque amplitudes and in electromechanical delay (P < 0.01). Post-hoc test revealed that torque amplitude differed between sexes only in the young (P < 0.001). In contrast, the electromechanical delay differed between sexes only in the elderly and the age-related elongation of electromechanical delay was significant only in women (P < 0.001). CONCLUSION: Both a sex difference and a sex difference of age-related change in hip abductor muscle properties were demonstrated. These sex differences may contribute to the sex difference in lateral balance performance.