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.
Coirault
C
C
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.
Riou
B
B
Pery-Man
N
N
Suard
I
I
Lecarpentier
Y
Y
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*