title: Dynamic muscle quality of the plantar flexors is impaired in claudicant patients with peripheral arterial disease and associated with poorer walking endurance.
abstract: OBJECTIVE
  Peripheral arterial disease and intermittent claudication (PAD-IC) negatively affects physical activity and function. There is evidence for plantarflexor muscle dysfunction and weakness; however, the extent to which this dysfunction can be attributed to reduced muscle size or quality, or both, is not yet known. This study investigated whether in vivo plantarflexor muscle quality during static and dynamic contractions is altered by PAD-IC and whether such changes are associated with impaired walking endurance according to initial and absolute claudication distances.
  
  
  METHODS
  The study recruited 22 participants, consisting of 10 healthy controls and 12 claudicant patients with occlusion of the superficial femoral artery (seven unilateral and five bilateral). Muscle quality of the combined gastrocnemius muscles during static contractions was calculated by normalizing the estimated maximal potential muscle force to the physiological cross-sectional area of the lateral and medial gastrocnemius. Muscle quality during dynamic contractions of the combined plantarflexor muscles was calculated as the ratio of peak voluntary concentric plantarflexor power and the summed volume of lateral and medial gastrocnemius.
  
  
  RESULTS
  Dynamic muscle quality was 24% lower in the claudicating-limb and asymptomatic-limb groups compared with controls (P = .017 and P = .023). The differences were most apparent at the highest contraction velocity (180°/s). Dynamic muscle quality was associated with reduced walking endurance (R = 0.689, P = .006 and R = 0.550, P = .042 for initial and absolute claudication distance, respectively). The claudicating-limb group demonstrated a trend toward reduced static muscle quality compared with controls (22%, P = .084). The relative contribution of the soleus muscle to plantarflexion maximum voluntary contraction was significantly higher in the claudicating-limb and asymptomatic-limb groups than in controls (P = .012 and P = .018).
  
  
  CONCLUSIONS
  The muscle strength of the plantarflexors in those with PAD-IC appears to be impaired at high contraction velocities. This may be explained by some reduction in gastrocnemii muscle quality and a greater reliance on the prominently type I-fibered soleus muscle. The reduced dynamic capability of the plantarflexor muscles was associated with disease severity and walking ability; therefore, efforts to improve plantarflexor power through dynamic exercise intervention are vital to maintain functional performance.
authors.affiliation: Department of Sport, Health and Exercise Science, University of Hull, Kingston upon Hull, United Kingdom; Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom. Electronic address: s.1.king@ljmu.ac.uk.
authors.forename: Stephanie
authors.initials: S
authors.lastname: King
authors.affiliation: Department of Sport, Health and Exercise Science, University of Hull, Kingston upon Hull, United Kingdom; Discipline of Exercise and Sport Science, University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Natalie
authors.initials: N
authors.lastname: Vanicek
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom; School of Sport, Health and Exercise Science, Bangor University, Bangor, United Kingdom.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: O'Brien
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D007383:Intermittent Claudication / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology*; D010147:Pain Measurement; D058729:Peripheral Arterial Disease / Q000175:diagnosis / Q000503:physiopathology*; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors; D016138:Walking