Perhaps this will help to explain my thoughts.
Zatsiorsky’s explosive strength deficit
As the resistance decreases and the motion time becomes shorter, the
difference between Fm (the maximal force reached in a given condition) and
Fmm (the highest among the maximal forces attained in the whole range of the
tested conditions) increases.
The difference between Fmm and Fm is termed the explosive strength deficit
(ESD).
ESD = 100 * (Fmm - Fm )/Fmm
ESD shows the percentage of an athlete’s strength potential that was not used
in a given attempt. In movements such as takeoffs and delivery phases in
throwing, ESD is about 50%. For instance, among the best shotputters during
throws of 21.0 m, the peak force Fm applied to the shot is in the range of 50
to 60 kg. The best results for these athletes in an arm extension exercise
(Fmm, bench press) are typically about 220 to 240 kg, or 110 to 120 kg for
each am. Thus, in throwing, they can only use about 50% of Fmm.
In principle, there are two ways to increase the force output in explosive
motions - to increase Fmm or decrease ESD. The first method brings good
results at the beginning of sport preparation. If a young shot-putter
improves achievement in, say, bench press from 50 to 150 kg and also pays
proper attention to the development of other muscle groups, this athlete has
a very strong basis for better sport performance in shotputting.
This is not necessarily valid, however, for a bench press gain from 200 to
300 kg. In spite of efforts devoted to making such a tremendous increase, the
shot-putting result may not improve. The reason for this is the very short
duration of the delivery phase. The athlete simply has no time to develop
maximal force (Fmm). In such a situation, the second factor, explosive
strength, not the athlete’s maximal strength (Fmm), is the critical factor.
By definition, explosive strength is the ability to exert maximal forces in
minimal time.
Let’s compare two athletes, A and B, with different force-time histories (Fig
2.9). If the time of motion is short (i.e., in the time deficit zone), then A
is stronger than B. The situation is exactly opposite if the time of the
movement is long enough to develop maximal muscular force. Training of
maximal strength cannot help athlete B improve performance if the motion is
in the time deficit
When sport performance improves, the time of motion turns out to be shorter.
The better an athlete’s qualifications, the greater the role of the rate of
force development in the achievement of high-level performance.
Neural (central) factors include intramuscular and intermuscular
coordination. Neural the level of intramuscular coordination, three main
option, are used by the CNS for varying muscle force production: recruitment
of MUs, rate coding, and synchronization of MUs (motor units). These can be
observed in well trained athletes during maximal efforts. The orderly
recruitment of MUs is controlled by the size of motoneurons (Hennemann’s size
principle): Small motoneurons are recruited first and requirements for higher
forces are met by the activation of the large motoneurons that in innervate
fast MUs. It seems that the involvement of slow twitch MUs is forced,
regardless of the magnitude of muscle force and velocity being developed. The
firing rate of the MUs rises with increased force production (rate coding).
The maximal force is achieved when (a) a maximal number of MUs is recruited,
(b) rate coding is optimal and © MUs are activated synchronously over the
short period of maximal effort.
The primary importance of intermuscular coordination for generating maximal
muscular force is substantiated by many investigations. Thus, the entire
movement pattern rather than the strength of individual muscles or single
joint movements should be the primary training objective. Explosive strength
(or rate of force development) and the force exerted in stretch-shortening
(reversible) muscle actions are independent components of motor function.
Time (and Rate of Force Development)
Because of the explosive strength deficit (ESD), maximal force F cannot be
attained in the time deficit zone. If the training objective is to increase
maximal force production (Fmm), there is no reason to use exercises in the
time deficit zone where Fmm cannot be developed. Furthermore, heavy
resistance exercises are not very useful for enhancing the rate of force
development in qualified athletes (Fig 6.3).
If the general objective of training is to increase force production in
explosive types of movement, in principle this can be done in one of two
ways. One option is to increase maximal force Fmm. This strategy, however,
brings good results only when the ESD is substantially less than 50%.
As an example, imagine two athletes who put a shot with a force of 500 N. The
first athlete can bench press a 120 kg barbell (roughly 600 N per arm). The
ESD for this athlete is [(600 - 500)/600] - 100 = 16.6%. This is an extremely
low value for shot-putting. The athlete has a great potential to improve
performance by increasing Fmm. Lifting a 200-kg barbell in the bench press
will surely lead to improvement in this individual’s performance. For the
other athlete, 1RM in the bench press is 250 kg. The ESD is (1250 -
500)/1250] - 100 = 60%. Further improvement of this athlete’s maximal bench
press, say to 300 kg, will not result in improvement in shot-putting
performance.
The second option for training to enhance force production is to increase the
rate of force development. Heavy resistance exercises are not the best choice
in this instance, especially for elite athletes. Special exercises and
training methods are a better alternative…