In vivo specific tension of human skeletal muscle

In this study, we estimated the specific tensions of soleus (Sol) and tibia lis anterior (TA) muscles in six men. Joint moments were measured during ma ximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imag ing, and pennation angles and fascicular lengths were measured using ultras onography. Tendon and muscle forces were modeled. Two approaches were follo wed to estimate specific tension. First, muscle moments during electrical s timulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths a t rest, and cadaveric fascicular lengths and pennation angles were used (da ta set B). The use of data set B gelded the unrealistic specific tension es timates of 104 kN/m(2) in Sol and 658 kN/m(2) in TA. The use of data set A, however, yielded values of 150 and 155 kN/m(2) in Sol and TA, respectively , which agree with in vitro results from fiber type I-predominant muscles. In fact, both Sol and TA are such muscles. Our study demonstrates the feasi bility of accurate in vivo estimates of human muscle intrinsic strength.