Harmonic and power spectrum analysis of vertical ground reaction force in patients who have a stroke within 3 months

Stroke remains a primary cause of disability globally. An in-depth comprehension of gait impairments following a stroke is vital for crafting effective therapeutic interventions, and vertical ground reaction forces (vGRF) provide valuable insights into these mechanics. Eighteen stroke survivors within 90 days post-stroke and 18 healthy controls participated in this study, completing a 2-min walking trial on an instrumented treadmill to investigate vGRF signals using harmonic and power spectrum analysis. Significant interactions were observed in vGRF patterns between stroke survivors and controls, and between paretic and intact legs. The paretic leg of stroke survivors exhibited a significantly lower harmonic coefficient $A_0$ (paretic: 61.71 ± 4.09% body weight vs. intact: 74.77 ± 6.65% body weight), a lower essential number of harmonics (paretic: 7.57 ± 1.12 vs. intact: 10.87 ± 1.76), a lower 99.5% power frequency (paretic: 4.19 ± 0.10 Hz vs. intact: 4.71 ± 0.31 Hz), and a higher median power frequency (paretic: 0.43 ± 0.03 Hz vs. intact: 0.40 ± 0.01 Hz) compared to the intact leg. The paretic leg demonstrated a simplified waveform shape (inverse U) compared to the intact leg (M shape), which likely contributes to the reduced essential number of harmonics and 99.5% power frequency, and the paradoxical increase in median frequency. These findings quantify the mechanical consequences of post-stroke neuromuscular deficits and highlight the potential of frequency domain analysis as a diagnostic tool, offering important implications for developing personalized rehabilitation strategies to improve outcomes in subacute stroke survivors.