## 2 Review of Model Construction and Parameter Determination
### Strength Constraints  
The force exerted by muscle has predominately been modeled in forward-dynamics simulation models using a muscle-tendon complex to divide the force-producing capabilities of muscle into a contractile component and two elastic elements: a series elastic element and a parallel elastic element [75]. Adopting the muscle-tendon complex approach requires mathematical relationships for each component so that the maximum force-generating capabilities of the individual can be calculated. While [PERSON] combined the sliding filament and cross-bridge theories to express the contractile force during muscle contraction at a microscopic level [76], the research focus of forward-dynamics simulation models has seen a macroscopic approach adopted to mathematically modeling the force produced by the whole contractile component as a function of its length, rate of shortening or lengthening, and \"neural\" activation [77]. The force-length relationship has been modeled as a quadratic function [9; 78] or bell-shaped curve [79], representing the ascending limb, plateau region, and descending limb [80; 81]. In the concentric phase of the force-velocity relationship, tetanic force decreases hyperbolically with increasing rate of shortening to approach zero at the maximum rate of shortening (modeled as a rectangular hyperbola) [82; 83; 84]. Eccentrically, the maximum force increases rapidly to around 1.4-1.5 (tetanic) [85] or 1.1-1.2 (voluntary) [86] times the isometric value, with the increasing rate of lengthening and then plateaus for higher speeds (modeled as an inverted hyperbola) [84]. These differences between tetanic and voluntary contractions are due to reduced neural drive under eccentric and low concentric maximum voluntary contractions [87; 88; 89]. The tetanic force-velocity relationship has been corrected for voluntary contractions via a differential activation function increasing from a depressed level at high eccentric velocities to full activation at high concentric velocities [79; 84; 90]. Discontinuity in the transition from eccentric to concentric [82] has been incorporated within the eccentric representation using predictions of the eccentric to concentric slope ratio [76; 84; 91; 92]. The series elastic component has commonly been modeled as a non-damped spring, with force expressed as an increasing function of its length and with a slack length below which no force can be generated [35]. The accuracy of series elastic component parameters has been shown to affect model performance [93], necessitating realistic elastic compliance. The force produced by the parallel elastic component has been assumed to be dependent on the contractile component length but independent of muscle activation [94]. Linear [95], parabolic [96], and exponential [97] functions have all been used to represent the parallel elastic component, although it has often been disregarded [8; 9] due to it having an assumed minimal effect during functional joint ranges of motion [98]. The application of structural constraints based on the muscle-tendon complex within forward-dynamics simulation models of maximal effort sporting movements have followed two alternative paths: muscle-driven models and torque-driven models. Muscle-driven models incorporate the effect of each muscle individually using the muscle-tendon complex representation. Although muscle-driven models have been widely used to investigate the function and contributions of individual muscles to different movements [99], their most frequently cited limitation is the difficult selection of realistic individual muscle parameters. Individual-specific muscle parameters, which are required for each component of each muscle-tendon complex, are difficult to determine non-invasively, whereas relying on data from the literature results in parameters that are not specific to any individual. Nonetheless, advances have been made in the scaling of musculo-tendon parameters such as optimal fiber length and tendon slack length for individual-specific models [100; 101; 102].