In this context, the authors also see potential in measuring two interacting neuromuscular systems to compare the two isometric muscle actions [44]. This requires even higher sensorimotor control of the neuromuscular system. Thus, it could provide additional information on control strategies during the two isometric muscle actions. The interaction depends, among other things, on the ability to synchronize the mechanical oscillations of the two neuromuscular systems [44]. The results of these measurements of interacting partners in relation to the two isometric muscle actions will be presented shortly. Isotonic contractions are performed with the movement of the joints and the length of muscle changes. Concentric contraction occurs with a shortening effect of the muscle and leads to joint movement (video 1.7 and 1.8). Isometric contractions are performed without joint movement and muscle length remains constant. The use of isometric contractions may be indicated when joint damage is present and joint movements are contraindicated or likely to increase pain (video 1.6), during early strengthening, when the limb is supported, or to promote blood circulation through alternating contractions.

Some functional activities also require isometric contractions (Fig. 1.3). A concentric contraction is a type of muscle contraction in which muscles shorten as they generate strength and overcome resistance. For example, if you lift a heavy weight, a concentric contraction of the biceps would cause the arm to bend against the elbow and lift the weight towards the shoulder. Cross-bridge cycling occurs and shortens the sarcomere, muscle fiber and muscles. When all this is combined, the first paradoxical result of significantly higher power in small frequency ranges during HIMA in MTG and vice versa the greater amplitude in fatigue while PIMA in MMG of the triceps muscle could be based on the assumption that eccentric muscle action is based on more complex neural control strategies. Thus, the present study suggests that HIMA may be more difficult to achieve compared to PIMA due to a more complex adaptation of the neuromuscular system. Indicators of this are the shorter endurance time and the higher performance of MTG vibrations in a small frequency range of 8 to 15 Hz as an indication of a stronger synchronization of muscle activation during HIMA. This, in turn, can affect the fatigue mechanism, but more research is needed to test this hypothesis.

Exemplary MMG signals from the triceps muscle. The isometric phases of the offset raw MMG signals of the triceps muscle during isometric muscle action (HIMA; top) and during isometric muscle pressure action (PIMA; bottom) are displayed at 80% of the MVC. The enlarged areas show a sequence of one second An eccentric contraction leads to the stretching of a muscle. Such contractions slow down muscle joints (act as “brakes” for concentric contractions) and can change the position of the load force. These contractions can be both voluntary and involuntary. During an eccentric contraction, the muscle expands under tension due to an opposite force greater than the force generated by the muscle. Instead of working to pull a joint towards muscle contraction, the muscle slows down the joint at the end of a movement or otherwise controls the repositioning of a load. Fig. 1.3. (A) Isotonic contractions (concentric and eccentric). (B) Isometric contractions.

The datasets used and/or analysed in this study are made available to the corresponding author upon reasonable request. In addition, Rudroff et al. [8] found higher glucose absorption during HIMA compared to PIMA in young men, but not in older men. Unlike isotonic contractions, isometric contractions generate strength without changing the length of the muscle, which is common in the muscles of the hand and forearm responsible for grip. With the example above, the muscle contraction required to grasp but not move a heavy object before lifting it would be isometric. Isometric contractions are often used to maintain posture. Isometric contraction occurs when muscle length remains relatively constant when tension is generated. For example, during a bicep loop, holding the dumbbell in a constant/static position rather than actively lifting or lowering it is an isometric contraction.21,22 Although the forces generated during isometric contractions are potentially greater than in concentric contractions, muscles are rarely injured during this type of contraction. Isometric exercises are often used in the early stages of rehabilitation of a muscle injury because the intensity of the contraction and the length of the muscle in which it contracts can be controlled.19 An eccentric contraction leads to the stretching of a muscle while the muscle still generates strength; In fact, the resistance is greater than the force generated. Eccentric contractions can be both voluntary and involuntary.

For example, a voluntary eccentric contraction would be the controlled lowering of the heavy weight increased during the above concentric contraction. An involuntary eccentric contraction can occur when a weight is too large for a muscle to carry, and is therefore slowly lowered under tension. Transverse cycling occurs even though sarcomas, muscle fibers and muscles lengthen and control muscle expansion. Isometric muscle contraction is the generation of muscle tension without changing muscle length or joint angle. The tension in the transverse bridges (the part of the myosin filament that pulls the actin filaments towards the center of the sarcomere during muscle contraction) is equal to the resistance force, which maintains a constant muscle length. Previous research suggests objective differences between the two hypothetical isometric effects. The most frequently found distinction is the “error of time to task” (i.e. the length of time the position or task of the force is maintained). Hunter et al. [9] conducted experiments that measure elbow flexor muscle fatigue in 15% of CVD in both isometric control tasks. The measurements showed a significantly longer duration during the force task (PIMA) compared to the position task (HIMA). These results were partially confirmed by Rudroff et al.

[6, 7]. Similar results were observed only at lower intensities (20 and 30% CVD) [6, 7] when the arm was positioned horizontally. At higher strength levels (45% and 60% CVD), no differences were observed between HIMA and PIMA [7]. If the forearm was positioned vertically, no difference was found at any intensity [6]. Relationship between the longest isometric phase and the entire isometric phase. The arithmetic mean and standard deviation are displayed when comparing PIMA (blue) and HIMA (grey). .