Evaluation of lower-limb muscle performance using amplitude, variability, and spectral characteristics during vertical jumping in basketball players

Abstract

Vertical jump is a key indicator for evaluating athletes' explosive power, neuromuscular efficiency, and fatigue resistance. Surface electromyography (sEMG) provides a non-invasive method to assess muscle electrical activity and is widely used in sports biomechanics and rehabilitation research. In this study, the electromyographic activity of the thigh and calf muscles—specifically the Rectus Femoris (RF), Gluteus Maximus (GM), Gastrocnemius Medialis (GMM), and Biceps Femoris Caput Longus (BFCL)—was analyzed during vertical jumps, focusing on amplitude, variability, and spectral characteristics. The study sample included 17 male athletes (mean ± SD: age 16.24 ± 1.2 years; height 179.6 ± 7.7 cm; weight 66.8 ± 14.4 kg). EMG signals were recorded using the FREEEMG system (BTS Bioengineering, Italy) at a sampling frequency of 1000 Hz and filtered within a 20–450 Hz bandwidth for analysis. Feature extraction, including RMS, MAV, VAR, WL, SSCR, MDF, and MNF, was performed using MATLAB R2024a (MathWorks, USA). The results indicated that the RF and GM were the primary contributors to explosive force during the jump's take-off phase, exhibiting stable RMS (0.10–0.11 mV) and MAV (120–130 µV) values consistently across all three trials. In contrast, the GMM and BFCL showed a gradual decline in both amplitude and frequency features (BFCL MDF ≈ 42.8 → 40.3 Hz; GM MDF ≈ 104.8 → 102.3 Hz), suggesting the onset of muscular fatigue. In terms of variability features (VAR, WL, SSCR, and ZCR), the GM and RF maintained stability even under fatigue, whereas the GMM and BFCL exhibited reduced signal complexity, likely owing to deactivation of fast-twitch (FT) fibers. The thigh muscles served as the primary generators of explosive force, while the calf muscles primarily contributed to stabilization and movement completion. The functional specialization of the muscles followed the order: GM ≈ RF > GMM > Biceps Femoris. These findings offer a scientific foundation for optimizing load distribution and monitoring fatigue in sports training.