Ann Clin Neurophysiol.  2024 Apr;26(1):8-13. 10.14253/acn.23009.

The amount of lower leg muscle and physical activity in patients with postural tachycardia syndrome

• Lee H
• Kim HA

• KMID: 2554848
• DOI: http://doi.org/10.14253/acn.23009

Abstract

Background
Resistance training for leg muscles is recommended for patients with postural tachycardia syndrome (POTS). However, no study has characterized the relationships between orthostatic symptoms, heart rate (HR) increase, and the mass of the lower leg muscle in patients with POTS. We sought to determine the relationships between the mass of the lower leg muscle, HR increase during the head-up tilt (HUT) test, and orthostatic symptoms in patients with POTS.
Methods
We prospectively enrolled 42 patients with POTS who were older than 16 years. The muscle mass was estimated using bioelectrical impedance analysis. We used the International Physical Activity Questionnaire-Short Form to measure self-reported physical activity. All patients were asked to complete the Korean version of the Orthostatic Grading Scale (KOGS).
Results
The HR increased during the HUT test by 38.7±7.88 beats/minutes. Both the HR increase during the HUT test and the total KOGS score were negatively correlated with the total metabolic equivalent of the task. The leg circumference and muscle mass were not correlated with the HR increase during the HUT test or the KOGS score.
Conclusions
The leg circumference and muscle mass were not related to orthostatic symptoms in patients with POTS. Cardiac remodeling or blood volume increase may be responsible for improvement in POTS after physical activity.

Keyword

Postural tachycardia syndrome; Orthostatic intolerance; Muscles; Leg; Postural tachycardia syndrome; Orthostatic intolerance; Muscles; Leg

Figure

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  Fig. 1. Correlation between the amount of physical activity and orthostatic intolerance. MET, metabolic equivalent; HR, heart rate; HUT, head-up tilt; KOGS, Korean version of the Orthostatic Grading Scale.

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  Fig. 2. Results from a path analysis model of the effect of physical activity on orthostatic intolerance. Physical activity exerted a significant direct effect on the total KOGS score, while the indirect effect mediated by leg muscle mass was not significant. The direct effect of the amount of physical activity on HR increase during the HUT test was not significant, as was the indirect effect mediated by leg muscle mass. MET, metabolic equivalent; KOGS, Korean version of the orthostatic grading scale; HR, heart rate; HUT, head-up tilt; GFI, goodness of fit index; AGFI, adjusted goodness of fit index; SRMR, standardized root mean residual.

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