Table 2 Definitions of principal terms

Muscle force estimation problem

Problem consisting in seeking a muscle effort estimation [1]. Muscle efforts are related to muscle force or muscle moment production

Solving strategy

Strategy chosen to solve the muscle force estimation problem which may or may not correspond to the physiological motor control

Forward solving strategy

Strategy chosen to solve the muscle force estimation problem which corresponds to the physiological motor control, i.e., from nervous drive to force production

Inverse solving strategy

Strategy chosen to solve the muscle force estimation problem which does not correspond to the physiological motor control, i.e., from the movement kinematics and external forces to muscle moment production

Muscle excitation

Nervous drive controlling muscle contraction [14]

Muscle activation

Rate of motor units’ recruitment within the muscle [14]

Type of problem

Designates the static or dynamic aspect of the solution sought to the muscle force estimation problem. In case where a single value of muscle force at a given time t is sought, the problem is a static type. Conversely, if a change of muscle force produced over time is sought, the problem is a dynamic type

Optimization method

Mathematical method used to solve the muscle force estimation problem

Time windows resolution

Designates the temporal aspect of optimization implementation. A discrete-time optimization searches for a solution for each temporal node individually. For continuous-time optimization, a solution is sought over the entire duration of the experiment in a single step

Static optimization

Process that allows an optimal solution to be found to a problem for which all the input data are known and can be processed independently of the time course [27]

Dynamic optimization

Process that allows an optimal solution to be found to a problem for which data being acquired and can’t be processed independently of the time course [28]

Experimental situation of interest

Period during which the acquired data correspond to the situation to which the study problem relates

Data tracking

Process that allows the tracking of experimental data to ensure the realism of muscle force estimation. Estimations are compared and adjusted to experimental data [1]