Author(s): ITO, K., OHTAKA, C., NAKATA, H., SHIBASAKI, M., Institution: NARA WOMEN'S UNIVERSITY, Country: JAPAN, Abstract-ID: 1822

INTRODUCTION:
Lower-limb complaints, such as muscle cramps, become more common with advancing age and can negatively impact quality of life. Previous surveys of adults aged ≥ 65 years found that the prevalence of leg cramps was 50% or higher [1]. Since leg cramps have been reported to be associated with peripheral vascular disease, age-related declines in peripheral circulation may contribute to their occurrence. Local heating of the lower limbs has been shown to acutely increase blood flow and improve endothelial function in older adults [2]. This study investigated whether passive calf-warming over an 8-week improves leg blood flow and alleviates leg muscle cramps in older adults.
METHODS:
Sixteen older adults aged ≥ 55 years (3 males, mean 67.8 years) who experienced leg cramps at least once per month participated in the experiment. The participants were provided with calf sleeves equipped with electric heating wires and skin thermometers. They were instructed to apply heat to both calves before bedtime for 30 min, 4–5 days per week, over an 8‑week period, raising the skin temperature to 40 ± 2°C. They also recorded leg cramp occurrences daily. Before and after the 8-week intervention, the participants visited the laboratory to assess their acute hemodynamic responses to the stimulus. Immediately before and during the calf warming, popliteal arterial blood velocity and diameter were measured via duplex ultrasonography to assess changes in blood flow waveforms and flows.
RESULTS:
Following 30 min of calf-warming, popliteal arterial blood flow significantly increased compared to pre-stimulation levels. Alterations in blood flow waveforms were also observed, resulting in a significant increase in the antegrade shear rate and a significant decrease in the retrograde shear rate. Continuous calf warming reduced cramp frequency, with a significantly lower frequency observed in the final week of intervention than in the first week. Furthermore, on the days after warming calves the previous night, the frequency of leg cramps tended to be lower than that on the days following non-heating.
CONCLUSION:
Local warming induces passive vasodilation of the muscular and cutaneous vasculature, thereby reducing vascular resistance, abolishing the retrograde component of blood flow, and increasing the popliteal arterial blood flow. Reductions in retrograde flow have been reported to be associated with improvements in endothelial function [3]; therefore, short-term and repeated local warming may improve endothelial function. Such vascular adaptations may have contributed to the observed reduction in the frequency of leg cramps. These findings suggest that both acute increases in blood flow and enhanced shear stress acting on the vascular endothelium, along with their chronic effects, are likely underlying mechanisms.
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2. Romero SA, et al. Am J Physiol Heart Circ Physiol 2017; 312(1): H89–H97.
3. Thijssen DHJ, et al. Hypertension 2009; 53(6): 986–992.