Electromyostimulation--a systematic review of the influence of training regimens and stimulation parameters on effectiveness in electromyostimulation training of selected strength parameters

Our first review from our 2-part series investigated the effects of percutaneous electromyostimulation (EMS) on maximal strength, speed strength, jumping and sprinting ability, and power, revealing the effectiveness of different EMS methods for the enhancement of strength parameters. On the basis of these results, this second study systematically reviews training regimens and stimulation parameters to determine their influence on the effectiveness of strength training with EMS. Out of about 200 studies, 89 trials were selected according to predefined criteria: subject age (<35 years), subject health (unimpaired), EMS type (percutaneus stimulation), and study duration (>7 days). To evaluate these trials, we first defined appropriate categories according to the type of EMS (local or whole-body) and type of muscle contraction (isometric, dynamic, isokinetic). Unlike former reviews, this study differentiates between 3 categories of subjects based on their level of fitness (untrained subjects, trained subjects, and elite athletes) and on the types of EMS methods used (local, whole-body, combination). Special focus was on trained and elite athletes. Untrained subjects were investigated for comparison purposes. The primary purpose of this study was to point out the preconditions for producing a stimulus above the training threshold with EMS that activates strength adaptations to give guidelines for implementing EMS effectively in strength training especially in high-performance sports. As a result, the analysis reveals a significant relationship (p < 0.05) between a stimulation intensity of ≥50% maximum voluntary contraction (MVC; 63.2 ± 19.8%) and significant strength gains. To generate this level of MVC, it was possible to identify guidelines for effectively combining training regimens (4.4 ± 1.5 weeks, 3.2 ± 0.9 sessions per week, 17.7 ± 10.9 minutes per session, 6.0 ± 2.4 seconds per contraction with 20.3 ± 9.0% duty cycle) with relevant stimulation parameters (impulse width 306.9 ± 105.1 microseconds, impulse frequency 76.4 ± 20.9 Hz, impulse intensity 63.7 ± 15.9 mA) to optimize training for systematically developing strength abilities (maximal strength, speed strength, jumping and sprinting ability, power).     

Incidence of exercise induced hypoxemia in elite endurance athletes at sea level

Recent evidence suggests that exercise-induced hypoxemia (EIH) may occur in healthy trained endurance athletes. However, at present, no data exist to describe the regularity of EIH in athletes or non-athletes. Therefore, the purpose of the present investigation was to determine the incidence of EIH during exercise in healthy subjects varying in physical fitness. Subjects (N = 68) performed an incremental cycle ergometer test to volitional fatigue with percent arterial oxyhemoglobin saturation (%SaO2) measured min-by-min. For the purpose of data analysis subjects were divided into three groups according to their level of physical training: 1) untrained (N = 16), 2) moderately trained (N = 27), and 3) elite highly trained endurance athletes (N = 25). EIH was defined as a %SaO2 of less than or equal to 91% during exercise. EIH did not occur in any of the untrained subjects or the moderately trained subjects. However, EIH occurred in 52% of the highly trained endurance athletes tested and was highly reproducible (r = 0.95; P less than 0.05). These findings further confirm the existence of EIH in healthy highly trained endurance athletes and suggests a rather high incidence of EIH in this healthy population. Hence, it is important that the clinician or physiologist performing exercise testing in elite endurance athletes recognize that EIH can and does occur in the elite endurance athlete in the absence of lung disease.     

Differences in H-reflex between athletes trained for explosive contractions and non-trained subjects

The efficacy of type Ia synapse on alpha-motoneurons of soleus and lateral gastrocnemius muscles has been investigated, using the H-reflex technique, in athletes engaged in sports requiring very rapid and intense contractions (sprinters and volley-ball players) as well as in non-trained subjects. It has been observed, in both muscles, that the ratio between the mean value of the maximal reflex response (Hmax) and the mean value of the maximal direct response (Mmax) elicited upon electrical stimulation of the tibial nerve is significantly smaller in athletes trained for explosive-type movements than in non-trained subjects. This difference in the Hmax: Mmax ratio was dependent on a smaller amplitude of Hmax and not on a greater amplitude of Mmax. No significant differences were observed between sprinters and volley-ball players. In both trained and non-trained subjects, soleus and lateral gastrocnemius muscles displayed significant differences in Hmax: Mmax ratio and Mmax amplitude but not in Hmax amplitude. Since the H-response is considered to be due mainly to activation of the smallest motoneurons in the motoneuronal pools, the difference in Hmax amplitude and Hmax: Mmax ratio between athletes and non-trained subjects could have been dependent on a lower incidence of these motoneurons in the athletes. This is in accord with the mechanical needs of muscles during explosive-type power training. Although this difference may have been wholly determined genetically, the possibility is discussed as to whether the lower incidence in sprinters and volley-ball players of small motoneurons could have been related to a training-induced transformation of small and slow motoneurons into large and fast ones.     

Comparison of responses to strenuous eccentric exercise of the elbow flexors between resistance-trained and untrained men

This study compared resistance-trained and untrained men for changes in commonly used indirect markers of muscle damage after maximal voluntary eccentric exercise of the elbow flexors. Fifteen trained men (28.2 +/- 1.9 years, 175.0 +/- 1.6 cm, and 77.6 +/- 1.9 kg) who had resistance trained for at least 3 sessions per week incorporating exercises involving the elbow flexor musculature for an average of 7.7 +/- 1.4 years, and 15 untrained men (30.0 +/- 1.5 years, 169.8 +/- 7.4 cm, and 79.9 +/- 4.4 kg) who had not performed any resistance training for at least 1 year, were recruited for this study. All subjects performed 10 sets of 6 maximal voluntary eccentric actions of the elbow flexors of one arm against the lever arm of an isokinetic dynamometer moving at a constant velocity of 90 degrees .s. Changes in maximal voluntary isometric and isokinetic torque, range of motion, upper arm circumference, plasma creatine kinase activity, and muscle soreness before, immediately after, and for 5 days after exercise were compared between groups. The trained group showed significantly (P < 0.05) smaller changes in all of the measures except for muscle soreness and faster recovery of muscle function compared with the untrained group. For example, muscle strength of the trained group recovered to the baseline by 3 days after exercise, where the untrained group showed approximately 40% lower strength than baseline. These results suggest that resistance-trained men are less susceptible to muscle damage induced by maximal eccentric exercise than untrained subjects.     

Effects of electromyostimulation training on muscle strength and power of elite rugby players

The present study investigated the influence of a 12-week electromyostimulation (EMS) training program performed by elite rugby players. Twenty-five rugby players participated in the study, 15 in an electrostimulated group and the remaining 10 in a control group. EMS was conducted on the knee extensor, plantar flexor, and gluteus muscles. During the first 6 weeks, training sessions were carried out 3 times a week and during the last 6 weeks, once a week. Isokinetic torque of the knee extensors was determined at different eccentric and concentric angular velocities ranging from -120 to 360 degrees .s(-1). Scrummaging and full squat strength, vertical jump height and sprint-running times were also evaluated. After the first 6 weeks of EMS, only the squat strength was significantly improved (+8.3 +/- 6.5%; p < 0.01). After the 12th week, the -120 degrees .s(-1) maximal eccentric, 120 and 240 degrees .s(-1) maximal concentric torque (p < 0.05), squat strength (+15.0 +/- 8.0%; p < 0.001), squat jump (+10.0 +/- 9.5%; p < 0.01), and drop jump from a 40-cm height (+6.6 +/- 6.1%; p < 0.05) were significantly improved. No significant change was observed for the control group. A 12-week EMS training program demonstrated beneficial effects on muscle strength and power in elite rugby players on particular tests. However, rugby skills such as scrummaging and sprinting were not enhanced.     

Maximizing strength development in athletes: a meta-analysis to determine the dose-response relationship

The efficiency, safety, and effectiveness of strength training programs are paramount for sport conditioning. Therefore, identifying optimal doses of the training variables allows for maximal gains in muscular strength to be elicited per unit of time and also for the reduction in risk of overtraining and/or overuse injuries. A quantified dose-response relationship for the continuum of training intensities, frequencies, and volumes has been identified for recreationally trained populations but has yet to be identified for competitive athletes. The purpose of this analysis was to identify this relationship in collegiate, professional, and elite athletes. A meta-analysis of 37 studies with a total of 370 effect sizes was performed to identify the dose-response relationship among competitive athletes. Criteria for study inclusion were (a) participants must have been competitive athletes at the collegiate or professional level, (b) the study must have employed a strength training intervention, and (c) the study must have included necessary data to calculate effect sizes. Effect size data demonstrate that maximal strength gains are elicited among athletes who train at a mean training intensity of 85% of 1 repetition maximum (1RM), 2 days per week, and with a mean training volume of 8 sets per muscle group. The current data exhibit different dose-response trends than previous meta-analytical investigations with trained and untrained nonathletes. These results demonstrate explicit dose-response trends for maximal strength gains in athletes and may be directly used in strength and conditioning venues to optimize training efficiency and effectiveness.     

Twitch contractile properties of plantar flexor muscles in power and endurance trained athletes

This study compared twitch contractile properties of plantar flexor muscles among three groups of 12 subjects each: endurance and power trained athletes and untrained subjects. The posterior tibial nerve was stimulated by supramaximal square wave pulses of 1-ms duration. Power trained athletes had higher twitch maximal force, maximal rates of force development and relaxation and also maximal voluntary contraction (MVC) force. The trained subjects had a smaller twitch maximal force: MVC force ratio and shorter twitch contraction and half-relaxation times than the untrained subjects with no significant differences between the two groups. Thus, the short time for evoked twitches in the athletes compared to the untrained subjects would seem unrelated to the type of training. It is concluded that power training induces a more evident increase of muscle force-generating capacity and speed of contraction and relaxation than endurance training. Accepted: 24 April 1999     

Relations between force-velocity characteristics of the knee-hip extension movement and vertical jump performance

Relations between force-velocity characteristics of the multijoint movement of the lower limbs and vertical jump performance were investigated. A total of 67 untrained subjects (age: 19.54 +/- 2.38 years; height: 166.88 +/- 8.53 cm; body mass: 59.14 +/- 10.82 kg, mean +/- SD) performed isometric and isotonic knee-hip extension movements on a servo-controlled dynamometer, and the force-velocity relations were determined. Also, vertical jump (VJ) performance was measured with a jump gauge. The force-velocity relation was described with a linear function so that the maximum isometric force (Fmax) and the maximum unloaded velocity (Vmax) for the knee-hip extension movement were estimated by extrapolation. Maximum isometric force coincided with maximum isometric force, F(0) (F(0)/Fmax = 1.03 +/- 0.24). Maximum isometric force, Vmax, and maximum power output (Pmax) were positively correlated with VJ (r = 0.48, 0.68, and 0.76, respectively; p < 0.001). However, when Fmax, Vmax, and Pmax were normalized with body mass (BM), leg length (LL), and BM, respectively, no correlation was seen between Fmax/BM and VJ (r = 0.24, p > 0.05), and significant correlations were seen between Vmax/LL and VJ (r = 0.56, p < 0.001) and between Pmax/BM and VJ (r = 0.65, p < 0.001). On the other hand, Fmax and Vmax (r = 0.12, p > 0.05) and Fmax/BM and Vmax/LL (r = 0.05, p > 0.05) were not significantly correlated, indicating that Fmax and Vmax were independent variables. The present estimates of Fmax, Vmax, and Pmax can be useful for evaluating the actual performance of multijoint movement of the lower limbs. It is suggested that, although in untrained individuals the speed of movement might be a more important determinant of jump performance, jump performance ability has a potential to improve with increases in strength of the lower limb.     

EMG, muscle fibre and force production characteristics during a 1 year training period in elite weight-lifters

The effects of a 1 year training period on 13 elite weight-lifters were investigated by periodical tests of electromyographic, muscle fibre and force production characteristics. A statistically non-significant increase of 3.5% in maximal isometric strength of the leg extensors, from 4841 +/- 1104 to 5010 +/- 1012 N, occurred over the year. Individual changes in the high force portions of the force-velocity curve correlated (p less than 0.05-0.01) with changes in weight-lifting performance. Training months 5-8 were characterized by the lowest average training intensity (77.1 +/- 2.0%), and this resulted in a significant (p less than 0.05) decrease in maximal neural activation (IEMG) of the muscles, while the last four month period, with only a slightly higher average training intensity (79.1 +/- 3.0%), led to a significant (p less than 0.01) increase in maximum IEMG. Individual increases in training intensity between these two training periods correlated with individual increases both in muscular strength (p less than 0.05) and in the weight lifted in the clean & jerk (p less than 0.05). A non-significant increase of 3.9% in total mean muscle fibre area occurred over the year. The present findings demonstrate the limited potential for strength development in elite strength athletes, and suggest that the magnitudes and time courses of neural and hypertrophic adaptations in the neuromuscular system during their training may differ from those reported for previously untrained subjects. The findings additionally indicate the importance of training intensity for modifying training responses in elite strength athletes.     

Analysis of biomechanical quantities during a squat jump: evaluation of a performance index

In this study, a procedure for evaluating the performance of an athlete in a squat jump has been developed. The athletes were divided into 2 categories according to their level of merit: elite athletes and non-elite athletes. In some of the subjects, the vertical component of acceleration during the squat jump was acquired with a uniaxial accelerometer. The acceleration-time curves obtained for each category of athletes were analyzed. Some analysis parameters suitable for establishing an athletic training level index were determined. A threshold value for this index that can be used to check gesture learning was also established, allowing the index to be used as a parameter for defining sport performance in a squat jump; thus it can also be used, during the training of an athlete, as the performance index to which reference should be made.     

Improving Sprint Performance in Soccer: Effectiveness of Jump Squat and Olympic Push Press Exercises

Training at the optimum power load (OPL) is an effective way to improve neuromuscular abilities of highly trained athletes. The purpose of this study was to test the effects of training using the jump squat (JS) or Olympic push-press (OPP) exercises at the OPL during a short-term preseason on speed-power related abilities in high-level under-20 soccer players. The players were divided into two training groups: JS group (JSG) and OPP group (OPPG). Both groups undertook 12 power-oriented sessions, using solely JS or OPP exercises. Pre- and post-6 weeks of training, athletes performed squat jump (SJ), countermovement jump (CMJ), sprinting speed (5, 10, 20 and 30 m), change of direction (COD) and speed tests. To calculate the transfer effect coefficient (TEC) between JS and MPP OPP and the speed in 5, 10, 20, and 30 m, the ratio between the result gain (effect size [ES]) in the untrained exercise and result gain in the trained exercise was calculated. Magnitude based inference and ES were used to test the meaningful effects. The TEC between JS and VEL 5, 10, 20, and 30 m ranged from 0.77 to 1.29, while the only TEC which could be calculated between OPP and VEL 5 was rather low (0.2). In addition, the training effects of JS on jumping and speed related abilities were superior (ES ranging from small to large) to those caused by OPP (trivial ES). To conclude, the JS exercise is superior to the OPP for improving speed-power abilities in elite young soccer players.     

Effects of mechanical vibration applied in the opposite direction of muscle shortening on maximal isometric strength

Most studies about human responses to mechanical vibrations involve whole-body vibration and vibration applied perpendicularly to the tendon or muscle. The aim of the present study was to verify the effects of mechanical vibration applied in the opposite direction of muscle shortening on maximal isometric strength of the flexor muscles of the elbow due to neural factors. Conventional isometric training with maximal isometric contractions (MVCs) and isometric training with vibrations were compared. Nineteen untrained males, ages 24 +/- 3.28 years, were divided into 2 training groups. Group 1 performed conventional isometric training and group 2 isometric training with mechanical vibrations (frequency of 8 Hz and amplitude of 6 mm). Both groups executed 12 MVCs with a duration of 6 seconds and 2-minute intervals between the repetitions. The subjects trained 3 times per week for 4 weeks. The strength of the group subjected to vibrations increased significantly by 26 +/- 11% (p < 0.05), whereas the strength of the group with conventional isometric training increased only 10 +/- 5% (p < 0.05). These data suggest that training with vibrations applied in the opposite direction of muscle shortening enhances the mechanism of involuntary control of muscle activity and may improve strength in untrained males. Since these findings were in untrained males, further studies with athletes are necessary in order to generalize the results to athletes' training, although it seems that it would be possible.     

Effect of one-legged exercise on the strength, power and endurance of the contralateral leg. A randomized, controlled study using isometric and concentric isokinetic training.

The purpose of this investigation was to study the effect of one-legged exercise on the strength, power and endurance of the contralateral leg. The performance of the knee extensor and flexor muscle of 20 healthy young adults (10 men and 10 women) was first tested by Cybex II+ and 340 dynamometers. Then 10 subjects were chosen at random to train using one leg three times a week for 7 weeks whilst the other 10 served as controls. During the 8th week, the tests were repeated. Both quadriceps and hamstring muscles of the trained subjects showed a cross-transfer effect from the trained limb to the untrained side. This concerned the strength and power, as well as endurance characteristics of these muscles. The average change in peak torque of the quadriceps muscle was +19% (P less than 0.001) in the trained limb, +11% (P less than 0.01) in the untrained limb and 0% in the control limbs. In hamstring muscles the changes were +14% (P less than 0.01), +5% and -1%, respectively. Concerning muscle endurance (work performed during the last 5 contractions in the 25-repetition test) the corresponding changes were +15% (P less than 0.01), +7% (P less than 0.01), and -1% in quadriceps muscle, and +17% (P less than 0.05), +7%, and -3% in hamstring muscles. The average strength benefit in the untrained limb was +36% (hamstring muscles) and +58% (quadriceps muscle) of that achieved in the trained limb. Untrained hamstring muscle showed better benefits in the endurance parameters than in strength or power parameters, while in the quadriceps muscle this effect was reversed. A positive relationship was observed between the changes (greater improvement in the trained limb resulted in greater improvement in the untrained limb) (hamstring muscles: r = 0.83, P less than 0.001, quadriceps muscle: r = 0.53, P less than 0.001). In endurance parameters, this relationship was almost linear while in the strength and power parameters the results were more in favour of a curvilinear relationship with limited benefit.     

Dissimilar effects of one- and three-set strength training on strength and muscle mass gains in upper and lower body in untrained subjects

The purpose of this study was to compare the effects of single- and multiple-set strength training on hypertrophy and strength gains in untrained men. Twenty-one young men were randomly assigned to either the 3L-1UB group (trained 3 sets in leg exercises and 1 set in upper-body exercises; n = 11), or the 1L-3UB (trained 1 set in leg exercises and 3 sets in upper-body exercises; n = 10). Subjects trained 3 days per week for 11 weeks and each workout consisted of 3 leg exercises and 5 upper-body exercises. Training intensity varied between 10 repetition maximum (RM) and 7RM. Strength (1RM) was tested in all leg and upper-body exercises and in 2 isokinetic tests before training, and after 3, 6, 9, and 11 weeks of training. Cross sectional area (CSA) of thigh muscles and the trapezius muscle and body composition measures were performed before training, and after 5 and 11 weeks of training. The increase in 1RM from week 0 to 11 in the lower-body exercises was significantly higher in the 3L-1UB group than in the 1L-3UB group (41 vs. 21%; p < 0.001), while no difference existed between groups in upper-body exercises. Peak torque in maximal isokinetic knee-extension and thigh CSA increased more in the 3L-1UB group than in the 1L-3UB group (16 vs. 8%; p = 0.03 and 11 vs. 7%; p = 0.01, respectively), while there was no significant difference between groups in upper trapezius muscle CSA. The results demonstrate that 3-set strength training is superior to 1-set strength training with regard to strength and muscle mass gains in the leg muscles, while no difference exists between 1- and 3-set training in upper-body muscles in untrained men.     

Effects of electromyostimulation training and volleyball practice on jumping ability

The aim of this study was to investigate the influence of a 4-week electromyostimulation (EMS) training program on the vertical jump performance of 12 volleyball players. EMS sessions were incorporated into volleyball sessions 3 times weekly. EMS consisted of 20-22 concomitant stimulations of the knee extensor and plantar flexor muscles and lasted approximately 12 minutes. No significant changes were observed after EMS training for squat jump (SJ) and counter movement jump (CMJ) performance, while the mean height and the mean power maintained during 15 seconds of consecutive CMJs significantly increased by approximately 4% (p < 0.05). Ten days after the end of EMS training, the jumping height significantly (p < 0.05) increased compared with baseline also for single jumps (SJ +6.5%, CMJ +5.4%). When the aim of EMS resistance training is to enhance vertical jump ability, sport-specific workouts following EMS would enable the central nervous system to optimize the control to neuromuscular properties.     

The effects of a calisthenics and a light strength training program on lower limb muscle strength and body composition in mature women

This study evaluated and compared the effectiveness of an aerobics-calisthenics (A-CAL) and an aerobics/weight training (A-WT) programs on lower limb strength and body fat (%). Thirty-five adult women (age 42.1 +/- 5.2 years) were randomly assigned to A-CAL (n = 14), A-WT (n = 14), or a control group (n = 7). The A-CAL and A-WT trained 3 days per week for 10 weeks. Maximal bilateral isometric and isokinetic knee extension (KEXT) and flexion (KFLEX) torque, squat jump (SJ), and body fat (%) were measured before and immediately after training. The results revealed nonsignificant differences between A-CAL and A-WT (p > 0.05). Both A-CAL and A-WT improved SJ (p < 0.001). A-WT increased isometric torque of KEXT and KFLEX (p < 0.05), isokinetic torque of KFLEX (p < 0.05), and decreased body fat (%) (p < 0.05) when compared with controls. In summary, the application of a 10-week light-weight training program improved selected strength parameters of healthy women, compared with controls, but the effectiveness of the calisthenics exercises as an independent form of strength training is dubious.     

Effect of multiple-load training on the force-velocity relationship

The effect of training with a combination of different loads (multiple-load training) on the force-velocity and force-power relationships was examined with training programs that included maximal isometric contraction (Fmax) and concentric contraction of the elbow flexor muscles. Twenty-one male college students were placed into 3 equal training groups (G(30 + 60), G(30 + 100), and G(30 + 60 + 100)) and performed multiple-load training 3 days per week for 8 weeks. The training load was a set fraction of the maximal isometric strength (% Fmax). The G(30 + 60) group performed 6 repetitions of elbow flexion at 30 and 60% Fmax. The G(30 + 100) group performed 6 repetitions at 30% Fmax and six 5-second Fmax loads. The G(30 + 60 + 100) group performed 4 repetitions at 30 and 60% Fmax and four 5-second Fmax loads. After training, Fmax and maximal velocity significantly increased (p < 0.05) in all 3 training groups. The increases in maximal power were significantly (p < 0.05) different between the G(30 + 60 + 100) group (52.9%) and the G(30 + 100) group (24.2%). These results suggest that multiple-load training programs with 4-6 repetitions are effective for improving muscle power and velocity of the elbow flexors.     

Do skill-based conditioning games offer a specific training stimulus for junior elite volleyball players?

This study investigated the specificity of skill-based conditioning games and compared the effectiveness of skill-based conditioning games and instructional training for improving physical fitness and skill in junior elite volleyball players. Twenty-five junior volleyball players (mean age +/- SE, 15.6 +/- 0.1 years) participated in this study. Heart rate data were collected on all players during the Australian Junior Volleyball Championships. After the competition, players were randomly allocated into a skill-based conditioning games group (n = 12) or an instructional training group (n = 13). Each player participated in a 12-week training program that included 3 organized court training sessions per week. No significant differences (P > 0.05) were detected between competition and skill-based conditioning games for the percentage of time spent in low-intensity, moderate-intensity, and high-intensity activities. Skill-based conditioning games induced improvements in vertical jump, spike jump, speed, agility, upper-body muscular power, and estimated maximal aerobic power, whereas technical instruction improved only spike jump and speed. Conversely, instructional training induced meaningful improvements in all measurements of skill, whereas improvements in technical skill after skill-based conditioning games were uncommon and typically small. The results of this study show that skill-based conditioning games offer a specific training stimulus to simulate the physiological demands of competition in junior elite volleyball players. Although the improvements in physical fitness after training were greater with skill-based conditioning games, instructional training resulted in greater improvements in technical skill in these athletes. These findings suggest that a combination of instructional training and skill-based conditioning games is likely to confer the greatest improvements in fitness and skill in junior elite volleyball players.     

Neuromechanical strategies employed to increase jump height during the initiation of the squat jump.

The maximal height attained in a vertical jump is heavily influenced by the execution of a large countermovement prior to the upward motion. When a jump must be executed without a countermovement, as in a squat jump, the maximal jump height is reduced. During such conditions, the human body may use other strategies in order to increase performance. The purpose of this research was to investigate the effects of two strategies employed during the initiation of the squat jump: the premovement silent period (PSP), and the small amplitude countermovement (SACM). Fifteen elite male volleyball players (20.6 +/- 1.6 years) and 13 untrained males (20.2 +/- 1.7 years) performed 10 maximal effort squat jumps from identical starting positions. The electromyographic activity of the vastus lateralis and biceps femoris was measured in conjunction with the vertical ground reaction force and vertical displacement. It was found that the presence of a PSP or a SACM of 1-3 cm did not increase maximal squat jump height significantly (p > 0.05), in neither the highly trained athletes nor the untrained individuals. These results suggest that these strategies do not play a major role in the determination of jump height. Researchers have assumed that a squat jump is purely concentric, and that there are no facilitating mechanisms present that may influence the performance of the jump. This study provides evidence to support this assumption.