title: A submaximal test for the assessment of knee extensor endurance capacity.
abstract: OBJECTIVE
  We aimed to develop an undemanding test for endurance capacity of the knee extensor muscles, which can also be applied to frail participants. We hypothesized 1) that the first objective indications for peripheral fatigue during incremental unilateral repetitive isometric knee extensor contractions could be used to assess a fatigue threshold (FT), 2) that torque at FT would depend on training status, and 3) that this torque could easily be sustained for 30 min.
  
  
  METHODS
  Five trained and five untrained participants performed 5-min bouts of 60 repetitive contractions (3-s on and 2-s off). Torque, set at 25% maximal voluntary contraction (MVC), was increased by 5% MVC in subsequent bouts. The highest torque for which rectified surface EMG remained stable during the bout was defined as the FT. On separate occasions, 30-min bouts were performed at and above the FT to assess sustainable torque. Changes in gas exchange parameters, HR, and RPE were monitored to corroborate FT.
  
  
  RESULTS
  At FT (RPE = 5.7 ± 1.7), torque was higher (P < 0.05) in trained (41.4% ± 5.8% MVC) than in untrained participants (30.5% ± 1.8% MVC). Sustainable torque was ∼4% higher than (P < 0.05) and significantly related to FT (r(2) = 0.79). When torque was increased by 5% MVC, significant increases in rectified surface EMG and V˙O2 were found.
  
  
  CONCLUSIONS
  During incremental knee extensor contractions, FT could be assessed at a submaximal exercise intensity. FT was higher in trained than in untrained participants and was related to exercise sustainability. With the use of FT, changes in endurance capacity of single muscle groups can potentially also be determined in frail participants for whom exercise performed until exhaustion is unwarranted.
authors.affiliation: MOVE Research Institute Amsterdam, VU University Amsterdam, THE NETHERLANDS.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: De Ruiter
authors.forename: Max I P
authors.initials: MI
authors.lastname: Mallee
authors.forename: Lara E C
authors.initials: LE
authors.lastname: Leloup
authors.forename: Arnold
authors.initials: A
authors.lastname: De Haan
mesh_terms: D000328:Adult; D004576:Electromyography; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006339:Heart Rate; D006801:Humans; D007717:Knee / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D010809:Physical Fitness; D011659:Pulmonary Gas Exchange; D052097:Quadriceps Muscle / Q000502:physiology*; D019415:Torque; D055815:Young Adult