gms | German Medical Science

Introduction: Running is known to cause urinary leakage in women with stress urinary incontinence (SUI) [1]. Small and large alpha-motoneurons of pelvic floor muscles (PFM) are recruited to match their contractile muscle properties to the impact of initial contact while running. The frequency content of electromyographic (EMG) signals enables estimating the activated types of alpha-motoneurons. Small alpha-motoneurons are responsible for the lower frequencies in the signal and large alpha-motoneurons for higher frequencies related to the recruitment of slow and fast muscle fiber types. Wavelet analyses of EMG signals allow the identification of activation intensity and frequency content in the range of a few milliseconds with high time resolution [2]. The evaluation of motor unit recruitment behavior of PFM at initial contact and in the pre- and post-initial contact phase sheds light on specific differences of involuntary reflexive activation patterns.

Objective: The purpose of this study was to evaluate the PFM EMG median frequencies using wavelet analysis at three different running speeds and to compare median frequencies (MF) of continent women and women with SUI.

Method: An EMG data analysis was performed on twenty-eight continent (CON) and twenty-one women with SUI. PFM EMG was recorded during 10 s at 7, 11 and 15 km/h treadmill running. EMG data were normalized to peak activity during maximum voluntary contraction. PFM EMG was analyzed with a continuous wavelet transform using Morse wavelets. To assess involuntary PFM activity, power spectra were extracted within six time intervals of 30 ms from -30 ms before to 150 ms after initial contact [3].

Results: The mean MF of each time interval showed no group differences. The mean MF varied between 73.9 and 88.2 Hz (SD: 12.2-18.3 Hz) in group CON and between 66.5 and 85.1 Hz (SD: 13.1-21.9 Hz) in group SUI. In the time interval 120-150 ms after initial contact, both groups showed significantly lower mean MFs during running at 15 km/h than during running at 7 km/h. The highest mean MFs were found in the pre-initial contact interval in both groups and in all speeds. In both groups mean MFs were significantly higher in the pre-activation phase than in the post-initial contact time intervals.

Conclusion: Although the groups did not differ significantly, differences in the motor unit recruitment behavior in the pre- and post-initial contact phase could be identified. The neuro-muscular control system reacts at each initial contact with muscular preparation and adaptation. Wavelet analyses made it possible to analyze this muscular anticipation a few milliseconds before initial contact. The higher mean MFs in the pre-initial contact phase identified a feed-forward adaption of PFM to the impact of the initial contact event. This was demonstrated by a higher content of recruited large alpha-motoneurons and a presumably faster PFM contraction in order to contribute to continence.

Conflict of interest: None