The obtained parameters suggest that the given conditioning contractions at 80% 1 RM were quite an efficient physiological phenomenon (PAP), observing the increase of variables of experimental groups. Special attention should be paid to the combined static-dynamic conditioning contractions in strength training (considering that no studies were found that dealt with this type of activation with external load, but only those that conducted combined static-dynamic stretching after different running sessions as a form of warm-up, and then evaluated various mechanical-motoric tests), because these stimuli showed their full efficiency in concentric phase of (CMJ) jump, unlike eccentric phases, in which the same stimuli had a irrelevant values.
The fact is that better performance after the application of combined conditioning contractions in concentric variable (the participant who lifted the imposed load in the concentric phase will be able to lower the external resistance in the eccentric phase, in terms of subtraction or addition of active, passive and viscous muscle components) should be associated with the stretching reflex mechanism, i.e., that explosive eccentric muscle actions subsequently activated the stretching reflex, as well as better storage of elastic energy in tendons and muscles, which increased muscle force production during the already mentioned consequential concentric actions (CMJ) H [26].
Since there were no instructions on the velocity or duration of the eccentric jump phase (Table 2), the obtained finding of variable (CMJ) H dd shows the participants had different performance strategies, which means that in some of the future similar research, it is necessary to conduct several familiarization sessions of (CMJ) jump. The authors [19, 20] indicated high levels of reliability when testing similar variables.
Possible factors that influenced the muscle force potential at (CMJ) jump (Fig. 1a, 1b) of the sample of student athletes (otherwise unaccustomed to the type of muscle strength training, i.e., different types of conditioning contractions), are peripheral factors such as muscle dimensions, or insufficient muscle capacity to produce force, which depends on the size of its physiological cross-section, or number of muscle fibers in the muscle, and on the cross-section of the fibers. Another possible factor is the hormonal status, since anabolic hormones accelerate the synthesis of muscle proteins from amino acids; the training changes in this case were exclusively cumulative, not acute. And the intramuscular coordination as a central (nervous) factor [41] probably had an impact on the mentioned results, primarily referring to insufficient synchronization of activation and deactivation of activated motor units, then changes in motor unit activation and motor unit activation to a greater or lesser extent.
Since muscle power is most often related to muscle velocity, these abilities will be observed as sublimated at (CMJ) jump (Fig. 2a, 2b and 3a, 3b). Positive results of muscle velocity of eccentric phases of vertical jumps can probably be explained by a higher share of fast muscle fibers (type II) compared to negative results of conditioning contraction groups, in which participants of slow muscle fibers (type I) predominated. However, only a muscle biopsy in a future study of the human-skeletal-muscle structure and its adaptations and regenerations could completely unravel all doubts.
Unlike the static and dynamic conditioning contraction groups that presented significant gains corresponded by rest intervals of 5 and 6 minutes between sets, the lower final values found in combined group can be explained by the fact that due to increased preload volume in students unaccustomed to this type of training, fatigue became the dominant factor with a negative impact on subsequent activities. Fatigue did not disappear at a faster rate than (PAP), so the potentiation of subsequent rapid movements could not be significantly achieved in a certain interval during the recovery period [32].
The study of the authors [15] on a sample of 8 trained and strength participants (which does not match the sample of the discussed study), assumed that heavy resistance exercises, containing 5 squats at 85% 1 RM, will lead to the increase in the height of the jump (primarily observed CMJ), which was performed in conditions (4 sets x 3 CMJ), as well as an increase in the electromyographic (EMG) activities of the subsequent plyometric exercises. Namely, first training group had a short rest interval and rest of 3, 10 and 20 minutes during the sessions, and the second control group had no rest in the first two sets). In the variable for vertical jump, no significant differences were found between the participants. However, the influence of the training treatment could not be completely ruled out, considering there were no negative effects of subsequent plyometric repercussions.
The possible explanation parameters the height of (CMJ) jump in the concentric phase (Fig. 4a, 4b) is as follows: 1) due to greater elongation of intrafusal muscle fibers, increased neuronal stimulation occurs, resulting in greater "provocation" of γ thinner muscle fibers of motor neurons in the reflex arc and thus signaling central nervous system (CNS), to increase the "trigger rates" of α thicker myelin fibers of anterior motor neurons, as physiological flexors, which lead to a possible increase in contractile muscle force [37], 2) increase in elongation of parallel (epimysium, perimysium, endomysium and sarcolemma) and serial muscle-tendon structures lead to increased elasticity, 3) the mechanism of improvement of key concentric muscle indicators occurs due to increased muscle force product, i.e. reduced displacement of myofibrils (Cohnheim᾿s fields) as a consequence of stored elastic energy in fibers and 4) as a possible mechanism of increased conditioning contraction, which probably has the greatest impact on improving concentric performance in consequent eccentric phases [6, 11].
Based on the previous findings, a study was found in which the authors [8], in the performance study attributed a superior benefit to isometric half-squats (3 x 3 sec.), compared to eccentric (70% 1 RM) and concentric (3 x 90% 1 RM) when increasing the rapid movement performance of the legs of the vertical (CMJ) jump, in the case when the impulse of the ground reaction force was equated between conditioning exercise.
Observed as sublimated, statistically significant progress, i.e., the largest increases in variables eccentric phases (CMJ) of jumps, were found after static and dynamic conditioning contractions. In contrast, concentric variables showed significant improvements in the combined and dynamic conditioning contraction groups. These facts both phases of the jumps, can be explained by a neuro-muscular coordination pattern of training sessions and jump testing process (originally referring to a group of dynamic stimuli).
Nowadays, the use of the term (PAP) may be inappropriate in some cases to frame the short-term responses that occur in voluntary gestures following a stimulation protocol. Therefore, some of the future papers should include some other research techniques, i.e., evaluation of neuro-muscular coordination patterns, such as electromyography, color Doppler,... considering the great importance of neural adaptations of the central nervous system (CNS) and peripheral nervous system that could affect muscle force, power, velocity,... because the effects so-called of post-activation performance enhancement (PAPE) can be attributed to vascular mechanisms, and increases in muscle temperature (responses found in a range of 5–15 minute).