Association of muscle performance and heart rate variability in middle-aged type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance, which impairs the metabolism of carbohydrates, lipids, and proteins. Recent findings indicate that skeletal muscle atrophy, decreased muscle strength, and reduced muscle performance have become prevalent complications of diabetes. Additionally, dysfunction of cardiac autonomic nerves also leads to skeletal muscle impairment. These issues further exacerbate diabetes, thereby leading to a vicious cycle. This study investigates the association between muscle performance and cardiac autonomic neuropathy in middle-aged T2DM patients.

In this case-control study, we included 51 diagnosed T2DM patients aged 30-55 years, with a duration of T2DM less than 5 years and HbA1C level below 8%. We also included 51 age-, sex-, and BMI-matched healthy control subjects. Muscle performance was assessed by evaluating the core endurance through the trunk flexor endurance test (TFET), trunk lateral endurance test (TLET), trunk extensor endurance test (TEET), along with hamstring muscle flexibility through the active knee extension (AKE) test. Cardiac autonomic function was evaluated using the heart rate variability test. Statistical analyses were performed using GraphPad Prism version 9. The Mann-Whitney test was used to compare the two groups, and data were represented as median (interquartile range). Values were considered statistically significant at P value ≤ 0.05.

We observed a significant decrease in core endurance (TFET, TLET, TEET) with P values < 0.001, as well as reduced hamstring muscle flexibility shown by a decrease in the degree of AKE test with P value < 0.001 in the T2DM patients when compared with the controls. Furthermore, heart rate variability in both time domain parameters (SDRR, CVRR, SDSD, RMSSD, pRR50%) and frequency domain parameters (Total power, VLF, LF, HF, LF/HF) also showed significant decreases, with P values < 0.001 in the T2DM group compared to the control group.

The observed decrease in muscle performance and heart rate variability parameters in middle-aged newly diagnosed T2DM patients suggests early skeletal muscle atrophy and cardiac autonomic dysfunction.