Ultrasound imaging measures of contraction characteristics of deep and superficial pelvic floor muscles differ during voluntary tasks

Aim: Pelvic floor muscles (PFM) are arranged in deep and superficial layers, Although the superficial layer is commonly considered with respect to sexual function, preliminary evidence shows coordinated contraction of layers during voluntary and involuntary tasks that challenge continence and organ support. This study aimed to investigate contraction characteristics of deep and superficial PFM layers across a range of tasks using transperineal ultrasound imaging (US). Seventeen females without pelvic floor dysfunction participated. Displacement of pelvic floor landmarks produced by contraction of deep and superficial PFM was measured from US images recorded during: submaximal voluntary contractions (two different verbal instructions), maximal voluntary contraction (MVC), and a ramped Valsalva manoeuvre. Times of onset and peak displacement of superficial PFM were earlier (0.29–0.36 s) than deep PFM during submaximal and MVC (P ≤ 0.01). Displacement amplitude was greater during MVC than submaximal tasks for deep (P < 0.001) but not superficial (P > 0.42) PFM. Shortening of deep PFM was sustained for longer (24.5(29.9) s longer; P < 0.005) and with greater steadiness during the MVC. During the ramped Valsalva, superficial PFM lengthened for most participants, whereas deep PFM shortened. In this task, shortening (when present) was less than for MVC and submaximal contractions (P < 0.05) Properties of contraction differed between deep and superficial PFM across tasks. In general, superficial PFM contracted rapidly but was poorly sustained, whereas deep PFM contracted slower but was maintained smoothly for long periods. These data of asymptomatic women provide a foundation to investigate contraction properties of these muscles in symptomatic populations.