title: Fatigue rate of the external anal sphincter.
abstract: OBJECTIVE
  Studies of skeletal muscle show that fatigue rate corresponds to the proportion of fast-twitch and slow-twitch fibres that are present in the muscle. Limited work has been done on the fatigue rate of the external anal sphincter. We have prospectively studied fatigability of the external anal sphincter in women with faecal incontinence and women with normal bowel control.
  
  
  METHODS
  Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. Fatigue rate was calculated from anal pressure measurements taken every 0.1 s over a 20-s squeeze.
  
  
  RESULTS
  Women with faecal incontinence (n=88, median -12 cmH(2) O/min) were less susceptible to fatigue than women with normal bowel control (n=36, median -43 cmH(2) O/min) (P<0.01). The external anal sphincter was less susceptible to fatigue with increasing age (P<0.01, r=0.499). In women with normal bowel control and in women with faecal incontinence fatigue rate was negatively correlated with maximum squeeze pressure (P<0.01, r=-0.287; P<0.01, r=-0.579).
  
  
  CONCLUSIONS
  The external anal sphincter was less susceptible to fatigue with increasing age. Women with faecal incontinence have a weaker but more fatigue-resistant external anal sphincter. This might correspond to a higher proportion of slow-twitch muscle fibres. Histological studies are needed to examine this hypothesis.
authors: Colorectal Surgery, South Manchester NHS Trust, UK. clairenockolds@btinternet.com
authors: C L
authors: CL
authors: Nockolds
authors: G L
authors: GL
authors: Hosker
authors: E S
authors: ES
authors: Kiff
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000502:physiology / Q000503:physiopathology*; D016022:Case-Control Studies; D005242:Fecal Incontinence / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008365:Manometry; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology; D011312:Pressure