The foundations for this topic can be found in the previous 4 articles in the series. Building off the understanding of viscoelastic tissues that are sensitive to the rate at which force is applied, we will examine training strategies designed to maximize muscle stimulation while avoiding injury. There are 3 types of muscle contraction:
Concentric – the muscle is shortening while contracting (the positive rep)
Isometric – the muscle does not change length while contracting
Eccentric – the muscle is lengthening while contracting (the negative rep)
It is widely misstated, and then repeated by others, that eccentric contractions produce more force than isometric contractions which produce more force than concentric contractions. This is not true. The force generated by muscle contraction is determined by the equation for torque reviewed in the last article, independent of the shortening or lengthening during contraction (minus a subtle detail – hysteresis – which is beyond the scope of our discussion). What people are confusing is the following…It is possible to apply a greater load (stress) to the muscle than the muscle can resist, even at maximum contraction, which will result in lengthening (strain) of the muscle = an eccentric contraction. A slightly lower stress applied to the muscle can equal the maximum contraction that the muscle is capable of without lengthening, and yet the muscle is incapable of shortening to move that load = an isometric contraction. If the load is reduced even further, the muscle is then capable of shortening while contracting against that stress = a concentric contraction.
Most injuries to the junction between muscle and tendon fibers or at tendon insertions to bone occur during eccentric contractions, but tissue injury can occur with any of the contraction patterns. Rarely during fitness training would one choose to apply a stress equal to the maximum that the muscle is capable of for a single contraction on the first repetition (the 1 rep max) since doing so just invites injury. There is no fitness training benefit to working near that threshold. The goal of fitness training is to apply stress to the muscle tissue, taking the muscle through cycles of contraction using all three patterns (eccentric, isometric, and concentric) until the point of muscle exhaustion where the applied stress eventually exceeds the muscle’s capacity, but only after a period of time.
The types of contraction used, the amount of resistance chosen, how many seconds each contraction (rep) lasts, the number of contractions in the set, the total time the muscle is under tension, rest intervals between sets, and the sequencing of the sets (supersets, drop sets, circuit training, etc.) are all variables that comprise one big equation. Setting up healthy training regimens tailored to individual needs involves manipulating these variables and others to produce the desired effect. That is the end goal we are working towards with these articles, but there is still more foundation to cover. Next issue: coordinating agonist and antagonist muscle groups, primary targets, and central stabilizers.
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