Strength is the ability to produce an external force. It can be measured in the gym by the maximum amount of weight that we can lift for a single repetition in a particular exercise. The ability to lift a weight in an exercise is determined by at least six separate factors, all of which can be altered by long-term training. We call the factors “strength mechanisms” and we call any changes to the factors “adaptations.”

1. Coordination - we can alter our strength by altering our coordination in an exercise. Our ability to coordinate an exercise is a measure of efficiency. The more coordinated we are in performing the lift, the more efficient we are, and the less muscle force we have to exert for a given amount of weight on the bar. Beginners often notice rapid strength gains, especially in complex exercises that require a high level of coordination like deadlifts and this is mostly caused by improvements in coordination that make them more efficient.
2. Antagonist muscle activation – we can alter our strength by altering the amount of muscle activation produced by the antagonist muscles at our joints. Antagonist muscles are those that oppose the movement of the agonists or prime movers. For example, the biceps brachii are antagonists in the bench press, since the elbow is extending and the biceps brachii are elbow flexors. A reduction in antagonist muscle activation increases the amount of turning force at the joint.
3. Agonist muscle activation - we can alter our strength by changing the level of agonist muscle activation and hence the number of muscle fibers inside a muscle that can be activated voluntarily during a maximal effort. Most muscles cannot be activated fully and we can typically only activate approximately 80% of the muscle fibers in large muscles during a maximal effort. Even so, training can increase this number and this increases our strength by allowing more muscle fibers to contribute to force production.
4. Hypertrophy - we can alter our strength by hypertrophy, which involves increasing the size of individual muscle fibers by adding extra myofibrils or new sarcomeres in series. These structures are responsible for producing force inside a muscle fiber, so adding more of them increases the total amount of force that a muscle can generate.
5. Tendon stiffness - we can alter our strength by changing the stiffness of the tendon that transmits the force from the muscle to the joint. If a tendon is compliant, the force transmission is often less effective. In contrast, when a tendon is stiff, the force transmission is more effective and this facilitates the production of a turning force by the joint.
6. Lateral force transmission - we can alter strength by altering how much force individual muscle fibers transmit to the tendon. Forces produced by muscle fibers are transmitted through the surrounding collagen and yet not every sarcomere of a muscle fiber has a strong connection to this collagen layer. The connections are produced by structures called costameres and these are added by strength training, leading to an increase in the amount of force transmitted by muscle fibers.

Conclusion

Strength is affected by at least six separate factors. Each factor can be targeted by different training methods, as follows. [1] Coordination can be improved by deliberate practice of the movement pattern and is especially affected by receiving coaching, watching videos of ourselves doing the movement, and focusing our attention on an external target during the exercise. [2] Antagonist muscle activation can similarly be reduced by employing an external focus of attention. [3] Agonist muscle activation can be increased by using a maximal effort while we are still unfatigued or minimally fatigued, which is why heavy loads are better than light loads for this purpose. [4] Hypertrophy occurs after a great variety of bodybuilding programs but the one thing they all have in common is achieving high levels of agonist muscle activation at the same time as a slow movement speed, since this is what exposes the fast twitch muscle fibers of the muscle to mechanical tension. [5] Tendons can be made stiffer by training with heavy (1-5RM) or moderately-heavy (6-10RM) loads since the external force is experienced at the joint by the tendon and this stimulates changes that make the tendon less compliant. [6] The amount of force that muscle fibers transmit laterally can be increased by adding more connecting structures. Unfortunately, exactly what makes this happen is unclear.