Effect of streptozotocin-induced diabetes on motoneurons and muscle spindles in rats.

This study examined the alterations in the number and size of motoneurons innervating the medial gastrocnemius (MG) and biceps femoris (BF) motor nuclei in diabetic rats (12 or 22 weeks after injection of streptozotocin) and age-matched controls using retrograde labeling technique. Additionally, morphological alterations of muscle spindles in BF and MG muscles were tested. Significantly fewer labeled MG motoneurons were found in 12- and 22-week diabetic rats as compared with age-matched control animals. In contrast, the number of BF motoneurons was preserved in each group. Compared to control animals, the ratio of larger motoneurons of MG and BF muscle were decreased at 12 weeks, and smaller MG motoneurons were drastically decreased at 22 weeks. Moreover, MG muscle spindle showed reduction of its number and increase of intrafusal muscle fibers; however, BF muscle spindles showed little or no difference from control animals. We conclude that there is an early loss of alpha motoneurons for both MG and BF muscles followed by a later loss of gamma motoneurons in MG muscle in diabetic animals. Moreover, loss of gamma motoneuron might induce atrophy of MG muscle spindles.

Characteristics of lower limb muscle activity during upper limb elevation in badminton players.

[Purpose] To clarify the characteristics of postural control in badminton players by examining their lower-limb muscle activity during upper-limb elevation. [Subjects and Methods] Fourteen badminton players and 14 non-players were studied. The subjects were instructed to perform an upper-limb elevation task in order to measure the activities of the biceps femoris and biceps brachii. [Results] When elevating the dominant hand, the mean biceps femoris integrated electromyogram showed markedly higher values in the player group, for the contralateral compared with the ipsilateral leg. Similarly, when elevating the dominant hand, the difference in the maximum integrated electromyogram response time between the ipsilateral and contralateral legs was significantly smaller in the players compared with non-players. [Conclusion] It may be possible to reduce the time needed to elevate the dominant hand by shifting lower-limb activity from the ipsilateral to the contralateral leg more quickly, while increasing the rate of rise in contralateral leg muscle activity.

Soleus H-reflex modulation during receive stance in badminton players in the receive stance.

[Purpose] This study aimed to clarify the characteristics of motor neuron excitability by examining the soleus H-reflex in the ready position adopted immediately before making a return during badminton games. [Subjects] Sixteen individuals with (badminton group) and 16 without (control group) experience of playing badminton were studied. [Methods] Each subject was instructed to take up various stances for returning a shuttlecock to measure the H- and M-waves in the soleus. [Results] The H-wave was significantly decreased when gripping a racket was held in the dominant hand than compared to just standing in the badminton group. In contrast, in the control group, no significant differences were observed between when standing and the other stances. [Conclusion] Based on these results, the excitability of spinal motor neurons may have been reduced (H-wave suppression) by badminton training to increase the instantaneous force (power training).

Characteristics of sway in the center of gravity of badminton players.

[Purpose] To clarify the characteristics of fluctuations in the center of gravity (CoG) of badminton players by comparing them between those with high and low performance levels. [Subjects] Eight male badminton players belonging to teams ranked among the top 3 at the All Japan Badminton Championships (high-level group) and 8 playing badminton for recreation in university clubs (low-level group) were studied. [Methods] CoG sway during two- and one (dominant and non-dominant)-leg standing with the eyes open and closed were recorded for 30 seconds, using a stabilometer. [Results] With their eyes open, the CoG was maintained near the center by the high-level group, while it was displaced in the direction of the dominant leg by the low-level group, with a significant difference between the two groups. In contrast, with the eyes closed, the trace length, sway area, and X- and Y-axis sway amplitudes were greater in the low- than in high-level group, with significant differences between the two groups. [Conclusion] These results support the usefulness of standing on the non-dominant leg with the eyes closed for the evaluation of badminton players' balance ability.