An index for breathlessness and leg fatigue.
ABSTRACT The features of perceived symptoms causing discontinuation of strenuous exercise have been scarcely studied. The aim was to characterize the two main symptoms causing the discontinuation of heavy work in healthy persons as well as describe the growth of symptoms during exercise. Breathlessness (b) and leg fatigue (l) were assessed using the Borg CR10 Scale and the Borg CR100 (centiMax) Scale, during a standardized exercise test in 38 healthy subjects (24-71 years). The b/l-relationships were calculated for terminal perceptions (ERI(b/l)), and the growth of symptoms determined by power functions for the whole test, as well as by growth response indexes (GRI). This latter index was constructed as a ratio between power levels corresponding to a very strong and a moderate perception. In the majority (71%) of the test subjects, leg fatigue was the dominant symptom at the conclusion of exercise (P<0.001) and the b/l ratio was 0.77 (CR10) and 0.75 (CR100), respectively. The GRI for breathlessness and leg fatigue was similar, with good correlations between GRI and the power function exponent (P<0.005). In healthy subjects, leg fatigue is the most common cause for discontinuing an incremental exercise test. The growth functions for breathlessness and leg fatigue during work are, however, almost parallel.
Article: Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups.[show abstract] [hide abstract]
ABSTRACT: The extent and characteristics of muscle fatigue of different muscle groups when subjected to a similar fatiguing task may differ. Thirteen healthy young men performed sustained contractions at 50% maximal voluntary contraction (MVC) force until task failure, with four different muscle groups, over two sessions. Per session, one upper limb and one lower limb muscle group were tested (knee extensors and thumb adductor, or plantar and elbow flexors). Changes in voluntary activation level and contractile properties were derived from doublet responses evoked during and after MVCs before and after exercise. Time to task failure differed (p<0.05) between muscle groups (220±64s for plantar flexors, 114±27s for thumb adductor, 77±25s for knee extensors and 72±14s for elbow flexors). MVC force loss immediately after task voluntary failure was similar (-30±11% for plantar flexors, -37±13% for thumb adductor, -34±15% for knee extensors and -40±12% for elbow flexors, p>0.05). Voluntary activation was decreased for plantar flexors only (from 95±5% to 82±9%, p<0.05). Potentiated evoked doublet amplitude was more depressed for upper limb muscles (-59.3±14.7% for elbow flexors and -60.1±24.1% for thumb adductor, p<0.05) than for knee extensors (-28±15%, p<0.05); no reduction was found in plantar flexors (-7±12%, p>0.05). In conclusion, despite different times to task failure when sustaining an isometric contraction at 50% MVC force for as long as possible, diverse muscle groups present similar loss of MVC force after task failure. Thus, the extent of muscle fatigue is not affected by time to task failure, while this latter determines the etiology of fatigue.Journal of Applied Physiology 03/2013; · 3.75 Impact Factor