title: A Short Submaximal Test to Determine the Fatigue Threshold of Knee Extensors in Young Men.
abstract: OBJECTIVE
  Recently, a fatigue threshold obtained during submaximal repetitive isometric knee extensor contractions was related to V˙O2max measured during cycling and to exercise endurance. However, test duration is quite long (20-30 min in young people) to be of practical and possibly clinical use. The purpose of the present study was to test the day-to-day reliability of a newly developed short test that assessed the fatigue threshold during a submaximal test with the knee extensors.
  
  
  METHODS
  Fifteen healthy young males were tested three times, once using the original long protocol (5-min blocks of repetitive unilateral isometric knee extensor contractions with stepwise (5% MVC) increases of force) and twice using a new shorter protocol. In the latter, force increased by 2% MVC every 30 s, starting at 15% MVC (all contractions were 3 s on, 2 s off). The fatigue threshold was defined as the force where the EMG/force ratio started to increase and, compared with the force, at which deoxygenated hemoglobin concentration ([HHb]) increased steeply (HHb threshold).
  
  
  RESULTS
  The EMG/force threshold during the short trials was reached after 3.9 ± 1.5 min of submaximal exercise and similar (P > 0.05) between days. The EMG/force threshold showed good reliability (intraclass correlation coefficient = 0.87, SEM = 2.2%) and did not differ between (P > 0.05) the short (31.1% ± 7.6% MVC) and long tests (30.5% ± 6.2% MVC), with a significant relation (r = 0.71) between both tests. Similar results (P > 0.05) were found for the HHb threshold.
  
  
  CONCLUSIONS
  In young healthy men, a fatigue threshold can be detected during repetitive isometric knee extensor contractions using a short submaximal test, which may be suitable for untrained or frail people and patients.
authors.affiliation: Research Institute MOVE, Vrije Universiteit Amsterdam, THE NETHERLANDS.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: De Ruiter
authors.forename: Philipp
authors.initials: P
authors.lastname: Hamacher
authors.forename: Bart G A
authors.initials: BG
authors.lastname: Wolfs
mesh_terms: D000328:Adult; D004576:Electromyography; D005080:Exercise Test; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption; D010807:Physical Endurance; D015203:Reproducibility of Results; D055815:Young Adult
chemical_list: D006454:Hemoglobins