How Strong is Human Muscle?

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This research was seeking to estimate the true maximum force that human muscle could generate. Professor Anthony J Sargeant wants the reader to understand that answering this question is not as simple as it seems!

In vivo specific tension of human skeletal muscle

Constantinos N Maganaris, Vasilios Baltzopoulos, Derek Ball, Anthony J Sargeant.

Journal of Applied Physiology
J Appl Physiol. 2001 Mar;90(3):865-72
Abstract
In this study, we estimated the specific tensions of soleus (Sol) and tibialis anterior (TA) muscles in six men. Joint moments were measured during maximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imaging, and pennation angles and fascicular lengths were measured using ultrasonography. Tendon and muscle forces were modeled. Two approaches were followed to estimate specific tension. First, muscle moments during electrical stimulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths at rest, and cadaveric fascicular lengths and pennation angles were used (data set B). The use of data set B yielded the unrealistic specific tension estimates 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 feasibility of accurate in vivo estimates of human muscle intrinsic strength
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Spinal cord injuries – paralysed leg muscles

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HL Gerrits carried out this research under the direction of Professor Anthony J Sargeant (Amsterdam) and Professor Maria Hopman (Nijmegen). It was part of a research collaboration on spinal cord injury between the two Universities (Vrije University Amsterdam, and the Radboud University, Nijmegen – in the Netherlands). Ms Gerrits went on to submit this published research paper as a chapter in her PhD thesis submitted under the supervision of Professor Tony Sargeant in the Vrije University.

 

Reproducibility of contractile properties of the human paralysed and non-paralysed quadriceps muscle

Gerrits HL, Maria T Hopman, Anthony J Sargeant, Arnold de Haan.

Clinical Physiology

Clin Physiol. 2001 Jan;21(1):105-13

Abstract
This study assessed the reproducibility of electrically evoked, isometric quadriceps contractile properties in eight people with spinal cord injury (SCI) and eight able-bodied (AB) individuals. Over all, the pooled coefficients of variation (CVps) in the SCI group were significantly lower (ranging from 0.03 to 0.15) than in the AB group (ranging from 0.08 to 0.21) (P<0.05). Furthermore, in all subjects, the variability of force production increased as stimulation frequency decreased (P<0.01). In subjects with SCI, variables of contractile speed are clearly less reproducible than tetanic tension or resistance to fatigue. Contractile properties of quadriceps muscles of SCI subjects were significantly different from that of AB subjects. Muscles of people with SCI were less fatigue resistant (P<0.05) and produced force-frequency relationships that were shifted to the left, compared with AB controls (P<.01). In addition, fusion of force responses resulting from 10 Hz stimulation was reduced (P<.05) and speed of contraction (but not relaxation) was increased (P<0.05), indicating an increased contractile speed in paralysed muscles compared with non-paralysed muscles. These results correspond with an expected predominance of fast glycolytic muscle fibres in paralysed muscles. It is concluded that quadriceps dynamometry is a useful technique to study muscle function in non-paralysed as well as in paralysed muscles. Furthermore, these techniques can be reliably used, for example, to assess therapeutic interventions on paralysed muscles provided that expected differences in relative tetanic tension and fatigue resistance are larger than approximately 5% and differences in contractile speed are larger than approximately 15%