Unilateral and Bilateral Resistance Training in Hypertension

Hypertension is one of the leading modifiable risk factors for cardiovascular disease and is strongly associated with autonomic nervous system dysfunction. Increased sympathetic activity and reduced parasympathetic activity contribute to impaired cardiovascular regulation, which can be assessed non-invasively through heart rate variability (HRV). Reduced HRV has been associated with increased cardiovascular morbidity and mortality. In addition to autonomic dysfunction, individuals with hypertension frequently exhibit reduced muscle strength, impaired functional capacity, and limitations in daily physical activities.

Resistance training is widely recommended as a safe and effective non-pharmacological intervention for hypertension because it improves blood pressure control, muscular fitness, and overall physical function. Although both unilateral and bilateral resistance training are commonly prescribed, their physiological effects may differ. Unilateral resistance exercises generally involve a smaller active muscle mass, potentially resulting in lower cardiovascular stress while maintaining local muscular adaptations. In contrast, bilateral resistance exercises recruit a larger muscle mass and may induce greater cardiovascular and hemodynamic responses. Despite these theoretical differences, evidence directly comparing their effects on cardiac autonomic regulation in individuals with hypertension remains limited.

The primary objective of this randomized controlled trial is to compare the effects of unilateral and bilateral resistance training on cardiac autonomic function assessed by HRV in adults with hypertension. Secondary objectives include evaluating changes in peripheral muscle strength, functional capacity, activities of daily living, and blood pressure following a supervised resistance training program.

Adults aged 40 to 75 years with a physician-confirmed diagnosis of hypertension who are able to participate safely in resistance exercise will be recruited from Munzur University and Tunceli State Hospital. After providing written informed consent, eligible participants will be randomly assigned to one of three groups using a computer-generated block randomization procedure with sex stratification:

Unilateral Resistance Training Group Bilateral Resistance Training Group Control Group

Participants allocated to the intervention groups will complete a supervised 12-week resistance training program performed twice weekly. Exercise intensity will be prescribed at 60-70% of one-repetition maximum (1RM). Both intervention groups will perform the same resistance exercises, including leg press, knee extension, leg curl, seated row, and chest press. The unilateral group will perform each exercise separately with the right and left limbs, whereas the bilateral group will perform the exercises simultaneously using both limbs. Each exercise session will consist of 2-3 sets of 8-12 repetitions with at least one minute of rest between sets. Training loads will be progressively increased when participants are able to perform more than 20 repetitions with a perceived exertion below 3 on the Modified Borg Scale.

Participants in the control group will not receive supervised resistance training during the 12-week intervention period but will receive standardized education regarding the health benefits of regular physical activity. Following study completion, participants in the control group will be offered the exercise intervention if the training program is demonstrated to be beneficial.

Outcome assessments will be performed at baseline and after completion of the 12-week intervention. HRV will be measured using a Polar H10 heart rate sensor connected to the Elite HRV application. Measurements will be obtained before exercise, immediately after exercise, and during the recovery period. Time-domain variables, including RMSSD, SDNN, pNN50, and mean RR interval, as well as frequency-domain variables, including total power, LF power, HF power, LF/HF ratio, LF peak frequency, and HF peak frequency, will be analyzed.

Peripheral muscle strength will be evaluated using one-repetition maximum testing for leg press, knee extension, leg curl, seated row, and chest press. Functional capacity will be assessed using the Six-Minute Walk Test (6MWT), while functional performance in activities of daily living will be evaluated using the Glittre Activities of Daily Living Test (Glittre-ADL). Resting and exercise blood pressure will be measured using a validated sphygmomanometer.

The study hypothesis is that unilateral resistance training will produce improvements in HRV, muscle strength, and functional capacity comparable to or greater than bilateral resistance training while imposing lower cardiovascular stress. The findings are expected to provide evidence supporting individualized resistance exercise prescription for individuals with hypertension and contribute to the optimization of exercise-based cardiovascular rehabilitation programs.