Types Of Muscle Contractions
Dynamic Contractions/Isotonic Contractions
Dynamic occur with movement or through the use of free weights. When an athlete lifts a free weight they are exerting a force against gravity. This contraction is often called an isotonic contraction. However, Isotonic implies that there is equal tension throughout the movement. This is inaccurate however, as the muscle tension changes in relation to the angle of flexion and since the angle of flexion changes throughout the movement the tension cannot be equal throughout. There are two types of dynamic contractions: 1) Concentric Contractions, 2) Eccentric Contractions
Concentric Muscle Contractions
A concentric muscle contraction occurs when a muscle shortens as the individual muscle fibres contract in order to overcome a force/resistance such as gravity. An example of a concentric muscular contraction is raising a dumbbell during a bicep curl – the bicep brachii contracts concentrically to work against gravity, as the muscle shortens it pulls the bones of the forearm decreasing the angle at the elbow.
Eccentric Muscle Contractions
An eccentric muscle contraction occurs when a muscle/muscle fibres lengthens/lowers (negative phase of lifting) whilst still under tension. This type of contraction normally occurs against gravity such as the lowering phase of a bicep curl or pull-up. During the lowering phase of a bicep curl the bicep contracts eccentrically (lengthens whilst under tension) to control the lowering/downward phase of the curl.
Eccentric muscle contractions are known to have greater force production – in simple terms it allows you to lower (in a controlled manner) a heavier weight than you would be able to lift. The greater force production during an eccentric contraction is believed to be due to greater recruitment of type II (fast twitch muscle fibres). Due to the greater force production it is often used as a training technique used to place a greater stress on muscle fibres. This can be done by performing negative reps whereby you take longer to lower the weight (e.g. 4secs) than you do to raise the weight (e.g. 2 secs) which places a greater overall strain on the eccentric phase. Another method is to perform supermaximum loads (loads greater than you can lift unaided) with assistance from a spotter who assists you on the positive phase whilst you lower the full weight eccentrically.
Eccentric contractions are known to induce greater levels of muscle damage and are often associated with delayed onset muscle soreness (DOMS). The extensive muscle fibre damage that can occur is believed by many to lead to increased protein synthesis as the muscle overcompensates for the damage resulting in muscle hypertrophy. One downside to the use of eccentric training is that it can result in a greater risk of injury.
Isometric Muscle Contractions
Isometric contractions occur when a muscle is contracted under static conditions (i.e. there is no lengthening or shortening of the muscle fibres) such as pushing against an immoveable object (a wall or a static rugby scrum) or whilst holding or carrying an object in static position (i.e. holding a dumbbell at the mid-way point of a bicep curl). With isometric contractions the resulting force is often greater than developed during a dynamic contraction. In this contraction a high force is developed without the muscle altering it's length.
Isokinetic Muscle Contractions
Isokinetic muscle contractions occur when a muscle contracts and shortens at a constant speed or constant angular speed. To perform Isokinetic muscle contractions you require specialist equipment - known as an Isokinetic Dynamometer - that increases the load when it senses the muscle is speeding up ensuring that the speed of movement is held constant throughout.
Benefits of Isokinetic Muscle Contractions:
1) Isokinetic exercises can be utilised to replicate the sport-specific speeds. This is believed to lead to improvements in neuromuscular coordination increasing the number of muscle fibres recruited as well as leading to improved efficiency. A good example is an isokinetic stationary bike that controls the speed to a set number of revolutions per minute.
2) Isokinetic muscle contractions lead to even gains in muscle strength throughout a muscles entire range of movement since the tension is at its maximum throughout the muscles range of movement.
3) By controlling the speed of movement the risk of injury can be greatly reduced and is particularly important during periods of rehabilitation following injury or surgery.
4) Can lead to improved muscle strength, endurance, cardiac fitness, and may have a positive effect on core muscles.