When is muscle tissue MOST vulnerable to injury if resistance is applied?

Muscle tissue is most vulnerable to injury when it is in a fully contracted state because at this point, the muscle fibers are shortened and any additional force applied can exceed their capacity to withstand tension. When a muscle is fully contracted, the actin and myosin filaments are maximally overlapped, leading to an optimal length for generating force. However, beyond this point, the muscle becomes susceptible to strains or tears if subjected to excessive resistance or load, as the fibers are already at their limit for elongation and tension generation.

In contrast, when muscle tissue is in a relaxed state, it can absorb force more effectively without the risk of injury, as the fibers are lengthened and less tension is present. Elongated muscle fibers also have some capacity to handle resistance because they are not at their extreme tension point, providing room for movement and flexibility. During mid-range contraction, the muscle is typically at a safer length for load application and can produce force without the same risk of injury as it would in full contraction.