Background: High-impact activities are often related to urine leakage in women, so deeper insight into continence mechanisms of pelvic floor muscles (PFMs) while running is needed. Therefore, simultaneous information about the intensity of PFM muscle activity and fibre recruitment behavior at each time point of the gait cycle can help in understanding PFM activity patterns.

Objective: We aimed to analyse spectral changes of the pre- and post-initial contact phase during running at 3 different speeds and to compare women with stress urinary continence (SUI) to those without SUI by using a wavelet approach.

Methods: PFM electromyography (EMG) was recorded during 7, 11 and 15 km/h treadmill running and analysed with Morse wavelets. The relative distribution of power was extracted during 6 time intervals of 30 ms, from 30 ms before to 150 ms after initial contact.

Results: We included 28 women without SUI (mean [SD] age 38.9 [10.3] years) and 21 with SUI (mean age 46.1 [9.9] years). The groups did not differ in power spectra for each time interval. However, we found significantly less EMG intensity in the lower frequency bands but more intensity in the higher frequency bands in the pre-initial contact phase than at post-initial contact.

Conclusion: Morse wavelets could be used to extract differences between pre- and post-initial contact activation behavior of PFMs during different running speeds as well as spectral changes toward high or low frequencies. This information sheds light on specific differences in involuntary reflexive activation patterns while running. Muscular preparation and adaptation a few milliseconds before initial contact could be helpful.