movement physiology: maximum load

yogabook / movement physiology / maximum load

Maximum load

In many non-cyclical and cyclical movements, the load varies over the working range. A maximum usually occurs at some point. Depending on the design of the exercise, the maximum load tends to depend on

  • intrinsic biomechanical factors such as the force-length-function of the muscles
  • external factors such as the angle between the direction of movement with the external weight and the direction of gravity (the vertical), which is usually the case for exercises with external weights such as dumbbells,
  • the physical nature of an aid, as in the case of a Theraband with its largely linear progressive resistance, which shifts the maximum load quite regularly to the end of the movement.

When designing an exercise, it is important to consider how the physical kinetics of the exercise should relate to the force-length-function of the muscles. If the physically greatest load and therefore a local load maximum lies in a very long sarcomere length, only a small weight can be moved, but the movement becomes easier in the direction of the center of the ROM. An example of this is the elbow joint flexion from the supine position. According to the kinetics of the exercise, the load decreases in the direction of the vertical of the arm down to zero. The rest of the ROM cannot be used for the exercise.

We see a different behavior with classic biceps curls: the initial elbow joint flexion with the arm vertical is absolutely light, the required force increases up to the horizontal forearm, which has the (global) maximum load, and decreases again with further flexion of the elbow joint. With the arm extended vertically, we see a global load minimum and with maximum flexion a local load minimum. The load maximum is halfway in the middle of the ROM, which accommodates the force-length-function and characterizes this exercise. If the upper body were tilted backwards, for example on an incline bench, the physical load maximum and the maximum force according to the force-length-function diverge further and further as the angle against the vertical increases. At a 45° incline, only 135° of the ROM can be used for the exercise, i.e. up to the vertical of the forearm, and only 90° in a flat supine position; the maximum load would then be when the arm is horizontal and extended, where the biceps have virtually no strength, as the theoretical zero point of the force-length-function is nearly reached here, which results from the lack of engagement of the myosin with the actin, and the lever arm of the biceps in the elbow joint is also very small, as the tendon runs very deeply in the joint area at this angle.

We see another situation with the so-called Scott curls, biceps curls performed on a desk at an angle of around 45°. At the beginning, the elbow joints are extended and the arm flexors have to lift against an already quite large horizontal lever of great sarcomere length. This is still feasible for the monoarticular brachialis, but the biarticular biceps are still close to the zero point of their strength. With the first flexion, the situation becomes increasingly more favorable for the biceps, but soon the forearm approaches the horizontal and thus the maximum effect of gravity. Only then does the movement become increasingly easier. Although the maximum physical load lies with the horizontal forearm, the initial lift-off is subjectively the heaviest.

The Theraband with its largely linear, progressive resistance often largely outweighs the physical effects and the influence of the force-length relationship or compensates for them to a certain extent, as is the case with a biceps curl performed with a Theraband whose attachment point is at an angle of 45° dorsally behind the hand of the outstretched arm in the starting position. The movement starts easily due to the low tension of the band, which accommodates the still low force of the arm flexors according to the force-length-function. At 45° flexion of the elbow joint, the band is perpendicular to the forearm and the physical lever arm is at its maximum, which largely offsets the increasing force according to the force-length-function, whose maximum at around 90° flexion of the arm is opposed to an already very high counterforce of the band. The lower lever arm of the forearm against the direction of pull then makes things easier.