Temperature dependence of soleus H-reflex and M wave in young and older women.
The purpose of this study was to investigate the effect of altered local temperature on soleus H-reflex and compound muscle action potential (M wave) in young and older women. H-reflex and M wave responses were elicited in 10 young (22.3 +/- 3.3 years) and 10 older (72.5 +/- 3.2 years) women at three muscle temperatures: control (34.2 +/- 0.3 degrees C), cold (31.3+/-0.5 degrees C) and warm (37.1 +/- 0.2 degrees C). H-reflex output, expressed as the ratio between maximal H-reflex and maximal M wave (H(max)/M(max)), was lower in the older, compared with the younger, group, regardless of temperature. In control temperature conditions, for example, the H(max)/M(max) ratio was 36.8 +/- 24% in the young and 25.4 +/- 20% in the older (P<0.05). Warming had no effect on the H-reflex output in either group, whilst cooling increased H-reflex output only in the younger group (+28%). In both groups, cooling increased (+5.3%), and warming decreased (-5.5%) the H-reflex latency. This study confirms that older individuals experience a reduced ability to modulate the reflex output in response to a perturbation. In a cold environment, for example, the lack of facilitation in the reflex output, along with a delayed reflex response could be critical to an older individual in responding to postural perturbations thus potentially compromising both static and dynamic balance.
Dewhurst
Susan
S
Department of Applied Physiology, University of Strathclyde, 76 Southbrae Drive, Jordanhill, Glasgow, G13 1PP, UK.
Riches
Philip E
PE
Nimmo
Myra A
MA
De Vito
Giuseppe
G
D000200:Action Potentials / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D000843:Ankle Joint / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography / Q000379:methods*; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D013696:Temperature