Complex training, also known as contrast training or post-activation potentiation training, involves the integration of strength training and plyometrics in a training system designed to improve explosive power. According to Jace Derwin: Complex training relies upon the performance of a strength exercise, often resistance based, followed by a plyometric exercise. The strength and the plyometric exercise are usually biomechanically similar i.e. they move through similar ranges of movement. For example, a back squat followed by a box jump; or a bench press exercise followed by a jumping clap push up. Such a combination is referred to as a pair or a contrast pair. The resistance based exercise will often be a near maximal effort- about 75-90% of the athlete’s maximal lift. The plyometric portion of the training should be completed in an explosive manner. Sets are often used. Between the performance of the strength exercise and the plyometric exercise there is between a 3-12 minute rest period; opinions vary on the most efficient length. As the muscles have been intensely activated by the strength exercise, this develops in the muscles a greater potential to apply force than they would have normally. This added potential to apply force is called post-activation potentiation (PAP). It is the fundamental basis of complex training. This potential to apply force, generated by the strength exercise, is utilised by the athlete in the plyometric exercise to boost their power output to a level greater than it otherwise would have been had they been doing plyometrics alone. In this way, the plyometric exercise can be performed more powerfully. For instance, an athlete may jump higher after they have completed a back squat at 90% maximal lift, had a rest for 3-12 minutes, and then jumped; as opposed to only jumping, where they would not get this improvement. The length of the rest period is chosen to be long enough to allow the athlete to recover after the strength exercise, whilst also being short enough to allow for the high degree of muscle activation to be utilised in the plyometric exercise.
By integrating plyometrics with strength training, there is an added benefit of improving rate of force, the speed with which force is achieved in movement.
The ambition in a complex training regime is not just to achieve better results in an individual workout but also to condition the athlete so they can perform more powerfully as a standard. Such an improvement again relies upon what Donald Chu calls the ‘neuromuscular connection’. That is the relationship between the intense activation of the nervous system and enhanced fast-twitch muscle fibre recruitment. However, in terms of long term training effects there is an added dynamic. And that is the conditioning of the body to adjust muscle fibres from slow to fast-twitch; thereby increasing the number of fast-twitch muscle fibres available for recruitment and with which to help power a given movement. Such a process is also referred to as muscle fibre type shifting. It is also often discussed in regard to converting muscle fibre types IIa to type IIb. Different training regimes can stimulate different muscle fibre type adaptions. For instance, as a result of their training body builders have a tendency to have relatively more type IIa muscle fibres which allow for forceful, but relatively slow movements. Whereas sprinters, as a result of their training, may have a larger amount of type IIb muscle fibres allowing for forceful, and relatively fast movements. Generally, the aim of complex training is to stimulate the athlete to develop more type IIb muscle fibres. This allows for their strength to be expressed quickly, which means greater power generation. In the context of rock climbing, and an isometric exercise preceding a plyometric one, Steve Maisch considers that one of the training goals of complex training is to operate at a level of fatigue thereby encouraging the body to learn to recruit from a wider range of muscle fibres in order to be able to apply the appropriate power. Thus, over a period of training, increasing the system strength and power output of the athlete as their body has learnt to recruit a larger number of muscle fibres. Studies on the effectiveness of complex training often last between 4 to 12 weeks and measure such abilities as vertical jump height and sprinting speed. Complex training often compares favourably to resistance only and plyometric only training programmes. There is apparently little information on longer term effects.