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Background: Although numerous studies revealed that isokinetic dynamometers were valuable tools for assessing spastic hypertonia, no standard methodology using such devices is currently widespread in clinical setting. The aim of this study was to standardize a protocol to assess spastic hypertonia in the triceps surae., Methods: The passive resistance during dorsiflexions imposed from 10 to 300 degrees /s with an isokinetic dynamometer was measured at the neutral position in 15 patients with spastic hypertonia and 12 healthy subjects. The normalized passive resistance was obtained by expressing raw passive resistance as a percent of the values measured at the lowest velocity (10 degrees /s). EMG signals from plantar and dorsiflexors were also recorded., Findings: While no significant difference between spastic patients and control subjects was observed in raw passive resistance values, the difference was significant for each tested velocity when considering the normalized values. Furthermore, the Ashworth score was significantly correlated with the normalized passive resistance for each velocity whereas no correlation was observed with the raw passive resistance. For the patients, except at the highest velocity, the normalized passive resistance was not affected by the fact that reflex responses in the triceps surae were elicited or not., Interpretation: The normalized passive resistance, expressed with respect to the initial one, i.e., measured at very low velocity, seems a very effective parameter to quantify the velocity-dependent increase in resistance to passive stretch in spastic plantarflexors. However, while the simplicity of the isokinetic tests and the reduced time of data treatment seems to support the clinical use of this methodology, further investigations are required to definitely standardize the protocol.

With the aim of proposing modelling equations for the length, force and shortening velocity of the triceps brachii, an X-ray and biomechanical study was carried out on the elbow joint. Two series of three upper right limbs removed from cadavers were used. It allowed us to situate the articular rotational axis of the elbow and to modelise the lever arm of the muscle group of the elbow extensors. Eight superimposed X-ray films with opaque markers at different articular angles show that the rotational axis of the elbow is different from the epitroch-lea-epicondyle axis, commonly localised by palpation and used as such in functional and biomechanical explorations. This rotational axis of the elbow, situated in the trochlea, is fixed at the centre of the articular range and moves noticeably to both extremities of this range. Biomechanical study, based on measurement of internal and external torques established using an overload, allowed us to modelize the lever arm of the triceps brachii between 0 and 2.44 radians, according to length of the ulna. The applications concerning length, force and shortening velocity of the triceps brachii are described. This method of modelling is applicable to other joints and muscle groups.

Changes in stiffness during stretch-shortening cycles were studied by applying prestretches of different rates and amplitudes on the tetanized sartorius muscle of the frog and measuring series elastic component characteristics during a subsequent quick release. Series elastic component stiffness was found to be dependent on the mechanical parameters of the stretching phase, and the so-called 'Cavagna effect' (increase in compliance) was rarely observed. The results are discussed in terms of improvement in muscle efficiency. Thus, an increase in stiffness during force generation will favour a better transmission of force and will reduce the coupling time whereas the opposite evolution during SEC recoil will allow a better release of potential energy.