Critical Review of Power Development

This post will provide a historical perspective for developing power/explosive strength, along with guidelines such as ‘optimal loads’ for developing power. Previous training studies investigating the ‘optimal load’ will be investigated as well as other practices for the strength & conditioning coach to consider.
Here, I present the ACSM & NSCA guidelines for developing power.
Velocity specificity of resistance training is one of the most contentious issues in the theory of muscle strength and power. Studies on isokinetic testing  and training methods have found  that strength increases are specific to the velocity at which one trains. If you train at a slow movement velocity, you tend to increase strength at that velocity, thus the improvements in strength at higher velocities, which are more common in sport, are usually not of the same magnitude. Based on this, it has been recommended that resistance training be performed at a high speed if the purpose of the training is to increase power.

Traditional resistance training may fall into 2 categories (1) training for maximum strength and / or Rate of Force Development (2) training for hypertrophy. Training for maximum strength involves lifting heavy loads (80-88% of 1-RM) for few repetitions (5-6) (Stone & O’Bryant, 1987). To induce hypertrophy loads are reduced (60-75% of 1-RM), but the number of reps increased.

Untrained subjects show rapids gains in strength, largely attributable to neural adaptations during the first 6-8 weeks of training. Subsequent gains in strength are accounted for by hypertrophy (e.g., 12 weeks of training). This also depends on training regime (i.e., number of reps, rest, etc.). The nervous system uses 3 options for varying muscle force production:

1.Motor unit recruitment (controlled by the size principle). Full Fast Twitch Motor Unit activation is difficult to achieve, particularly with untrained people. Athletes engaged in strength & power training show increased motor unit activation.

2.Firing rate/ rate coding – rate of electrical impulses to the motor unit resulting in contraction

3.In order to reach maximum force levels the fast twitch motor units must be recruited.

Normally, motor units work asynchronisation to produce a smooth accurate movement. With strength training increases in speed of recruitment (e.g., time between type fibre recruitment is reduced) can possibly occur. There is some evidence that in very fast contractions that the recruitment sequence is altered and high threshold motor units are recruited simultaneously with low threshold motor units.

In conclusion, maximum muscular force is achieved: by 1. A maximum number of both Slow Twitch & Fast Twitch fibres are activated, 2. Rate coding is optimal, 3. motor units work as simultaneously as possible and 4. Relaxation of the antagonists.
Rate of force Development: In practice, sport performance frequently involves rapid ballistic movement at a speed further along the movement velocity spectrum. Indeed, studies have reported that while heavy load weight training enhanced strength, it resulted  in negligible  improvement in power or performance (Bloomfield et al., 1990). It has been reported (Schmidtbleicher & Buerle, 1987; Schmidtbleicher, 1993) that when loads of 90-95% 1-RM and 2-4 Reps are performed RFD or power and movement speed can be improved to a greater extent than using relatively light loads. These findings are based on the size principle of motor-unit recruitment (Schmidtbleicher, 1988). Hence, conflict in the literature as to what training strategy should used to enhance RFD. Is it (a) the use of heavy loads, high force and therefore according to the size principle of motor unit recruitment, greater recruitment of fast twitch motor units; or (b) train at a speed which is similar to the competitive performance to maintain specificity. Research (Wilson et al., 1993, Fell et al, 2003) favours the later, but in practice athletes will and should incorporate the both heavy and light loads.
The problem of the deceleration phase in traditional resistance exercises can be overcome if the athlete throws or jumps with the weight. Dynamic (Ballistic) resistance training is a strategy where relatively light loads (approx 30% 1-RM) are lifted at high speed and accelerated throughout the movement (i.e., Bench Press throws, Jump Squats). This training method has been shown to be highly favourable than traditional resistance training in improving a wider range of performance capacities (Wilson et al., 1993, Fell et al., 2003).

There are several factors that affect the ‘optimal load’ for power development, including:
- Measurement differences (transducer, force platform, or both; inclusion & exclusion of body mass; reporting of average or peak power)
- Strength level of athletes
- Training status of athlete within yearly training cycle
- Nature of the exercise assessed
To increase force output and velocity and reduce fatigue within a set, some specific methods have evolved over the years. Recent research indicates that, compared to the traditional manner of performing repetitions, repetitions presented using clusters or the rest-pause or breakdown methods can increase force or velocity. Clusters are a method in which a set of higher repetitions is broken down into smaller clusters of repetitions that allow a brief pause between each of these clusters. For example, 8 repetitions can be performed as 4 clusters of 2 repetitions with a 10-second rest between clusters. The rest-pause system is similar but typically entails the breakdown of a lower repetition set (i.e., 5RM) into single repetitions with a short pause (i.e., 2-15 seconds) between repetitions. A breakdown (also known as stripping) set consists of small amounts of resistance being taken from the barbell during short pauses between repetitions. This reduction in resistance to accommodate the cumulative effects of fatigue results in a decreased degree of deterioration in power output across the set, as well as increased force for the initial repetitions as compared to the traditional manner of lifting a heavy resistance.

Haff et al., (2003) investigated the effect of 3 types of set configurations (cluster, traditional, and undulating) on barbell kinematics during a clean pull for 1 set of 5 repetitions at 90 and 120% 1RM. Significantly higher peak velocity occurred during the cluster set when compared with traditional sets at both intensities, whilst peak displacement was significantly higher than traditional sets at 120% intensity.
Whether the resistances should be presented in an ascending (working up in load) or descending (working down in load) order during training has been cause of some debate (Baker, 2001). A recent study examining the effects of ascending and descending order on power output during bench throws reported that an ascending order resulted in the highest power output during bench throws (Baker, 2001). An ascending order of resistances with the inclusion of a lighter down set may be an effective method of presenting power training loads.
The basic finding for this study is that the absolute power output for the workout is highest when using an ascending order, but that power output during lifting lighter resistances is higher using a descending order. For sports where movement speed and power output against lighter external resistances is more important than overall maximal power, then the descending order may prove a better method of presenting loads during power training. In sports where maximal power output against large resistances is more important as in rugby and American football, then the ascending order may be more beneficial. If a coach is seeking to train power across the spectrum of resistances, then performing sets in ascending order with a lighter down set at the end could be a simple method of attaining these goals.

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