Mechanics of human quadriceps muscle.
Mechanics of human quadriceps muscle strips (vastus lateralis; n = 10) were investigated over the whole load continuum. Mechanical experiments were performed at 29 degrees C and in both twitch and tetanus modes. For a given level of isotonic total load (P) and over a large part of the contraction phase, instantaneous velocity (V) was shown to be a unique function of instantaneous length (L), regardless of time and initial length. By considering this time- and initial length-independent mechanical property between instantaneous L and instantaneous V over the whole P continuum, a three-dimensional P-V-L relationship was constructed. Any variations in stimulation conditions modified the time-independent P-V-L diagram. Such modifications in the P-V-L relationship were characteristics of changes in contractile performance. Moreover, characteristics of the P-V relationship were investigated in both twitch and tetanus modes. The curvature of the P-V hyperbola was significantly higher in tetanus at 30 Hz than in twitch mode (P < 0.001). In conclusion, our study indicates that, in human quadriceps muscles, contractility can be defined as the time- and initial length-invariant part of a three-dimensional P-V-L relationship. Moreover, our data are consistent with an increase in economy of force generation in tetanus contractions compared with that in twitches.
Institut National de la Santé et de la Recherche Médicale Unité 275-Laboratoire d'Optique Appliquée-Ecole Nationale Supérieure des Techniques Avancées-Ecole Polytechnique, Palaiseau, France.
C
C
Coirault
B
B
Riou
N
N
Pery-Man
I
I
Suard
Y
Y
Lecarpentier
D000328:Adult; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology*; D007551:Isotonic Contraction / Q000502:physiology*; D008297:Male; D008838:Microcomputers; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*