MUSCULAR FORCE IN 3D by Nicolas de LUSSY, qualified Civil Engineer and Physiotherapist

I observed, twenty-six years ago, that HUXLEY and HANSON’s sliding filament theory presented a balance of muscle forces that was incompatible with functional anatomical data. Starting from this this impossible equilibrium, in 2014 I described three major inconsistencies in the hypothesis of longitudinal traction produced by muscle unit shortening and I outlined the basis of an alternative hypothesis – that myosin heads pushing on actin filaments would produce muscle motor force by expansion [11].

As a development of the central theme of my article of 5th October 2014 [11], I present below the experiment conducted and the visible, consistent results taken from an independent thesis that I have since undertaken in collaboration with the EPF School of Engineering, Sceaux [2] [10]. The experiments, observations and models of this hypothesis have all conformed this new orientation in understanding how skeletal muscle mechanical forces are transformed.

MUSCULAR FORCE IN 3D by Nicolas de LUSSY, qualified Civil Engineer and Physiotherapist

Based on the fact that the increase in sarcomere diameter is not taken into account in current theory [10], let us look at the following hypothesis: muscle efficiency is determined by expansion of the motor units which change the form of the inextensible fibres of the muscle envelope that run through the muscle, pushing them aside and thus providing stability for and actuation of the connected osseous segments (fig.1).


According to the current theory relating to skeletal muscle fibre contraction [5][12], it is generally acknowledged that all skeletal muscles can only function as a result of sarcomere shortening, that there is no change in transversal diameter [9, p.375] and that muscle fibres are cells that are specifically intended to contract (in a linear direction for skeletal muscle fibres) [4, p.96]. This sliding filament muscle contraction model was proposed by Hanson and Huxley [8] in 1955. Muscle performance was deemed to be the result of tractive force, or longitudinal centripetal force (Lcl) produced by linear shortening of the actin and myosin motor units [7] transmitted via a flexible tendon to the muscle attachment point to the bone.


However, this theory of longitudinal centripetal force alone has not been confirmed in experimentation. Let us take the example of a 10kg load raised by a human arm.

The human arm possessing normal angular elbow mobility, with under-arm support provided to the upper member, can activate the lower arm to move from extension (180°) to flexion (90°) while holding a 10kg weight, (fig. 2). It is clear that (fig. 3) when longitudinal centripetal force is used to activate a lever, it has no effect in initiating or closing extension (fig. 4). However, if push-force, or transversal centrifugal force (Tct) is used, the lever is systematically actuated (fig. 5) over the entire angular range.


figure 2 figure 3 figure 4 figure 5

Physiological action Test description Action using Lcl Action using Tct

If the sarcomere produces a transversal centrifugal force, there is a clear result: the increase in diameter must be visible, both on a macroscopic and a microscopic scale.

Macroscopically, the biceps expands under effort, a clear fact visible to all.

Under the microscope, this increased sarcomere transversal diameter was already visible in 1954 in HUXLEY and HANSON’s shots of an experimental series of sarcomere contractions (1/2/3/4 and 10/11) [7], (fig.6), Figure 6

and in the contractions observed in their muscular histology film in 1959 [3],(fig. 7)

Figure 7


The increase in the sarcomere transversal diameter can still be observed today in the life science experiment proposed by J.J. AUCLAIR, professor of Life Sciences [1] (fig.8) and on fibres stimulated under optical microscope by Professor Shannon Meadows.[12]

From this recurrent observation of expansion, the conversion of transversal centrifugal force must be compatible with the sarcomere’s structural elements [13][9].

Figure 8

3D behavioural modelling [2][10], taking account of the mechanical properties of the sarcomere components, [13][9] confirms the increase in transversal diameter, broken down here in two 2D diagrams:

Cross-section: the motor unit is a set of twisted proteins, actin and myosin. They are arranged in a harmonious overall structure, a series of lines forming a “Z” shape. The specific feature of this accordion or bellows-like configuration is that it is mechanically conducive to increasing the height of the structure [2] [11] and [10] (fig.9).

Figure 9 Figure 10

Lateral view: as the actin filaments are arranged in a hexagonal shape around the myosin filament, they move apart under the effect of transversal centrifugal force starting from the myosin filament. [2][11] and [10], (fig.10).

The hypothesis of tractive force being produced by longitudinal centripetal force alone is not confirmed in this experiment. Conversely, the experiment did confirm the pertinence of push-force being generated by transversal centrifugal force alone. Moreover, observation and 3D modelling also provide further evidence to support this hypothesis.

A motor unit is principally expansive [11] and not contractile (1954 theory) [7][8].

This opens up a whole new dimension of biomechanics [11], already partially explored [6], by consolidating the consistency of muscle chains. It also heralds common interests with industry whereby a new type of actuator using transversal centrifugal force (fig. 11) for levers could be offered.

Figure 11

Références bibliographiques :

[1] AUCLAIR J.J., 2010, “fibre contractée à vide”, personal pages, orange

[2] ANQUEZ J. et al., 2015, Modelling and verification of N. de Lussy’s hypothesis relating to the behaviour of muscle cells, 3rd year project, EPF Engineering School, Sceaux


[4] CROSS P.C. and MERCER K.L., 1995, “Cell and tissue ultrastructure. Functional approach”, De Boeck, 420p. (

[5] DUKE T. and JULICHER F., 2000, “Motor proteins: the cell’s workforce”, in “Images de la Physique”,

[6] GAGEY Q. and PILLU M, 2013, SYSTEMES MUSCULAIRES COMPLEXES, (Complex muscle systems), University Pars 11

[7 HANSON J. and HUXLEY H.E 1954Changes in the cross-striations of muscles during contraction and stretch and their structural interpretation”, Nature.

[8] HUXLEY J.E., 1955, “The structural bases of contraction in striated muscle”, Symp. Soc. Exp. Biol., vol. 9: p.228-264

[9] KARP G., 2004,”Cell and molecular Biology”, De Boeck, 852 p. (

[10] LEVAL R. et al., 2014, “Humanoid robot”, 3rd year project, EPF Engineering School, Sceaux

[11] LUSSY (de) , 2014, ” Le bodybuilder le sait, le muscle gonfle” (The bodybuilder knows – muscle expands), www.structurothé
[12] MEADOWS S., “Skeletal Muscle Cell Contraction”, video recorded by Roane State Community College,

[13] SZENT-GYOGYI A.,1951 “Chemistry of Muscular Contraction” (2nd edit., Academic Press, N.Y., 1951).