Mechanical efficiency during repetitive vertical jumping

The purpose of this study was to compare mechanical efficiency between repeated static jumps (SJ), countermovement jumps (CMJ), drop jumps from 75% of maximum CMJ jump height (75DJ) and drop jumps from 125% of maximum CMJ height (125DJ). Subjects included eight jump-trained males. All subjects completed 30 continuous repetitions in the SJ, CMJ, 75DJ, and 125DJ. Oxygen consumption, peak force and center of mass displacement for each repetition during the four jumping patterns were measured. ME was calculated from a combination of force-time curves, displacement-time curves and lactate-corrected oxygen consumption values. In addition, muscle activity was recorded from the vastus medialis, vastus lateralis and biceps femoris using surface electromyography (EMG). 125DJ and 75DJ resulted in significantly (P ≤ 0.05) greater ME in comparison to CMJ and SJ. CMJ resulted in significantly greater ME in comparison to SJ. In addition, braking phase muscle activity was significantly greater in 125DJ and 75DJ in comparison to CMJ. Negative work was significantly different between 125DJ, 75DJ and CMJ (125DJ > 75DJ > CMJ). There was a significant positive correlation (r = 0.68) between ME and negative work performed across 125DJ, 75DJ and CMJ. These findings suggest that stretch-shortening cycle movements, which include a strenuous braking phase combined with simultaneous high muscle activity, increase ME. This may be due to optimal muscle-tendon unit kinetics and usage of stored elastic energy.     

Differences in mechanical efficiency between power- and endurance-trained athletes while jumping

Mechanical efficiency (ME) of jumping exercises was compared between power-trained (n = 11) and endurance-trained athletes (n = 10) using both a biomechanical and a physiological approach. In drop jumps and in stretch-shortening cycle exercise on a special sledge (sledge jumps), the subjects performed 60 muscle actions from a dropping height of optimum minus 40 cm (O – 40), as well as from dropping heights of optimum (O) and optimum plus 40 cm (O + 40). Thus, they were tested in six different tests which lasted for a total of 3 min for each. The mean ME values in the drop jumps from the lowest dropping height upwards were as follows: 23.8 (SD 5.3)%, 35.5 (SD 10.8)% and 39.2 (SD 6.6)% for the power group, and 30.8 (SD 6.5)%, 37.5 (SD 8.7)% and 41.4 (SD 7.0)% for the endurance group. In the sledge jumps the ME values were 37.0 (SD 5.6)%,48.4 (SD 4.0)% and 54.9 (SD 8.5)% for the power group, and 40.2 (SD 5.9)%, 46.9 (SD 5.7)% and 58.5 (SD 5.5)% for the endurance group. As can be seen, the ME values increased with increasing stretch load. However, the groups did not differ from each other except in the drop jump condition of O – 40 (P < 0.05). The higher power (P < 0.001) among the power athletes in every measured condition was associated with a faster rate of electromyogram development during the pre-activity, and smoother muscle activity patterns in the ground contact. On the other hand, the endurance athletes had a lower blood lactate concentration after every test, and in addition a lower heart rate and ventilation during the sledge jumps than their power counterparts. Therefore, it would seem that the similar mean ME values between the subject groups could be explained by improved function of the neuromuscular system among the power group and improved metabolism among the endurance group.     

Mechanical efficiency of locomotion in females during different kinds of muscle action

Summary The mechanical efficiencies (ME) of pure positive and pure negative work as well as of stretch-shortening cycle (SSC) exercise were investigated with a special sledge apparatus. The subjects were 20 young females who performed six different types of submaximal exercise: two of pure concentric exercise (positive work), two of pure eccentric exercise (negative work) and two SSC exercises. The work intensities were determined individually, from the recordings of distance obtained during a single maximal concentric exercise. Each exercise involved 60 muscle actions lasting a total of 3 min per testing condition. The MEs of pure positive work with intensities of 30% and 60% maximum (C₃₀ and C₆₀ respectively) were 15.5%, SD 2.6% and 14.3%, SD 1.9%, respectively. In pure negative work, when the dropping heights were 20 cm (E₂₀) and 80 cm (E₈₀), MEs were 28.4%, SD 6.9% and 47.9%, SD 10.1%, respectively. In SSC-exercise, the MEs during the positive phase of the take-off were 31.3%, SD 6.3% (E₂₀/C₉₀) and 35.0%, SD 7.0% (E₈₀/C₆₉). The total MEs in SSC-exercise were 29.1%, SD 4.0% (E₂₀/C₉₀) and 40.1%, SD 5.2% (E₈₀/C₆₀ × 100). In pure negative work, the increased stretching velocity increased the value of ME. In the concentric phase of SSC-exercise, the integrated electromyographic activity (iEMG) of vastus lateralis (VL) and vastus medialis (VM) muscles were lower (P<0.05) than in pure concentric work, when the mechanical work was the same (C₆₀ vs E₈₀/C₆₀). During pure eccentric work, iEMGs were lower in comparison to the eccentric phase of SSC-exercise. The EMG activity of VL, VM and soleus muscles was potentiated in SSC-exercise during the eccentric phase of the take-off, when the dropping height was 80 cm. The results of the present study demonstrate the role of stretch reflexes as an increasing factor of ME in the positive work of SSC-exercise, when prestretch intensity is high enough. When muscle stiffness increases via reflex pathways, it may also increase the elasticity of the muscles and decrease their metabolic demands.     

Influence of aging on the mechanical behavior of leg extensor muscles

Summary Age dependence of the mechanical behavior of leg extensor muscle was investigated using vertical jumps with and without a stretch-shortening cycle on the force-platform. A total 226 subjects (113 females and 113 males) ranging in age from 4–73 years were examined. The results indicated in general that performance in males was better than that in females. This difference was reduced when body weight was taken into consideration. The peak performance of the various parameters, such as average force, height of rise of center of gravity, net impulse, and also the average power output, was reached in both sexes between the ages of 20 and 30 years. For example, the average vertical force in squatting had the following mean values in the various age groups of the male subjects: 114 N (4–6 years), 402 N (13–17), 618 N (18–28), 508 N (29–40), 435 N (41–49), 320 N (54–65), 315 N (71–73 years). When the jumps were performed using the stretch-shortening cycle, the potential of the mechanical performance after prestretching was also sensitive to aging in a similar manner. The results suggest that it is not only the performance of pure concentric contraction that is influenced by the maturation and aging processes but, the that elastic behavior of muscle and reflex potentiation are also affected by the same processes.Supported in part by a grant No. 8318/78/78 from the Ministry of Education, Finland     

Interaction between pre-landing activities and stiffness regulation of the knee joint musculoskeletal system in the drop jump: implications to performance

The purpose of the present study was to investigate the interaction between the pre-landing activities and the stiffness regulation of the knee joint musculoskeletal system and the takeoff speed during a drop jump (DJ). Nine healthy male subjects performed a DJ test from the height of 50 cm. The surface electromyographic (EMG) activity of the vastus lateralis (VL) muscle was recorded to evaluate both the pre-landing and post-landing muscle activation levels. Simultaneous recording of the jumping motion and ground reaction force was performed by a high-speed video camera (100 frames·s^–1), and a force platform was employed to allow joint moment analysis. Joint stiffness was calculated by a linear regression of the knee joint moment/angle relationship. Elasticity of the knee extensor muscle during DJ was estimated by means of a four-element muscle model consisting of a parallel elastic component, a series elastic component (SEC), a viscous damper, and a contractile element. DJ performance correlated positively with the positive peak power of the knee joint (P<0.01) and with the moment of the knee joint at the end of stretch (P<0.01). However, there was no significant relationship between DJ performance and the positive peak power of the ankle joint. The knee joint moment at the end of stretch correlated with the SEC stiffness during the transmission phase from the end of the initial impact to the onset of the concentric action (P<0.01) and with the maximum rate of isometric force development of the knee extensors (P<0.01). Multiple regression analysis showed that the SEC stiffness during the transmission phase of the knee joint can be explained by a combination of the pre-activity of the VL muscle and the knee joint angular velocity at touchdown (F=5.76, P<0.05). These results seem to emphasize the functional significance of the pre-programmed activity for controlling the subsequent stiffness regulation and then contributing to the performance in DJ. Thus, it can be suggested that the centrally pre-programmed activity and the associated elastic behavior of the SEC in the knee extensor muscle in conjunction with the muscle contractile property play a major role in regulating the performance in DJ. Electronic Publication     

Neuromuscular function and mechanical efficiency of human leg extensor muscles during jumping exercises

The influence of prestretch amplitude on the mechanical efficiency was examined with 5 subjects, who performed 5 different series of vertical jumps, each of which differed with respect to the mechanics of the knee joint action during the prestretch (eccentric) phase of the contact on the floor. Electromyographic activity was recorded from the major extensor muscles during the entire work period of 1 min per series. In addition, expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that high net efficiency of 38.7% was observed in condition where amplitude of knee bending in eccentric phase was small. In large range motion the corresponding net efficiency was 30.1%. In jumps where no prestretching of extensor muscles ocurred the net efficiency was 19.7%. The high efficiency of small amplitude jumps was characterized by low myoelectrical activity of the leg extensor muscles during the positive (concentric) work phase. In addition, the small amplitude jumps had shorter transition time in the stretch-shortening cycle, high average eccentric force and high stretching speed. Therefore the results suggest that the restitution of elastic energy, which was also related to the length change and stiffness of the muscles during stretch, plays an important role in regulating the mechanical efficiency of work.     

Use of a Kin-Com dynamometer to study the stretch-shortening cycle during plantar flexion

Summary The aim of this study was to evaluate the Kin-Com II dynamometer in the study of the stretch-shortening cycle (a concentric muscle action preceded by an eccentric muscle action). Measurements were made of plantar flexion at different angular velocities (120° · s^–1 and 240° · s^–1) with the knee at two different angles (0° and 90°). Ten healthy women ranging in age from 22 to 41 years were studied. Torque values were recorded simultaneously with surface electromyograms (EMG); maximal voluntary concentric torque values were recorded and, after a short rest, the torque values of the concentric action which followed immediately after an eccentric action of the same velocity, both with maximal effort. Mean values were taken at different ankle positions and also averaged over different ranges. A concentric action preceded by an eccentric action generated a torque value on an average about 100% larger than a concentric action alone. The EMG activity was lower or unchanged. It was concluded that the present method could be useful in the study of the stretch-shortening cycle in plantar flexion and in the testing of the behaviour of the elastic components in people with disabilities in the lower limbs.     

Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency

The net mechanical efficiency of positive work (η_pos) has been shown to increase if it is immediately preceded by negative work. This phenomenon is explained by the storage of elastic energy during the negative phase and its release during the subsequent positive phase. If a transition time (T) takes place, the elastic energy is dissipated into heat. The aim of the present study was to investigate the relationship between η_pos and T, and to determine the minimal T required so that η_pos reached its minimal value. Seven healthy male subjects were tested during four series of lowering–raising of the body mass. In the first series (S ₀), the negative and positive phases were executed without any transition time. In the three other series, T was varied by a timer (0.12, 0.24 and 0.56 s for series S ₁, S ₂ and S ₃, respectively). These exercises were performed on a force platform sensitive to vertical forces to measure the mechanical work and a gas analyser was used to determine the energy expenditure. The results indicated that η_pos was the highest (31.1%) for the series without any transition time (S ₀). The efficiencies observed with transition times (S ₁, S ₂ and S ₃) were 27.7, 26.0 and 23.8%, respectively, demonstrating that T plays an important role for mechanical efficiency. The investigation of the relationship between η_pos and T revealed that the minimal T required so that η_pos reached its minimal value is 0.59 s.     

Effects of stretch-shortening cycle training on mechanical properties and fibre type transition in the rat soleus muscle

The effects of exercise training on mechanical properties and fibre type transitions have been investigated in rat soleus muscle. The exercise was a repetition of stretch-shortening cycles. A method of dual controlled releases was applied to obtain tension/extension curves, which characterize the elastic behaviour of the series elastic component (SEC), and the force/velocity relationship characterizing the contractile elements. Other contractile measurements included: contraction time (t _c), half-relaxation time (t _1/2) and twitch/tetanus ratio (P _t/P _o). Additionally, the muscle fibre type composition was determined by a classical histochemical method. A 12-week period of training induced a significantly higher percentage of fast-twitch fibres and a lower percentage of slow-twitch fibres (P<0.01). This fibre adaptation led to a significant (P<0.01) decrease in t _c and an increase in maximum shortening velocity (V _max). An increase in compliance of the SEC was also observed. This elastic adaptation is interpreted in terms of modification of the active components of the SEC. All the histochemical and mechanical data presented in this study show that rat soleus muscles trained by stretch-shortening cycles acquired faster characteristics. Thus the results confirm that a slow-twitch to a fast-twitch fibre transition is obtainable in mature rats.     

Estimation of errors in mechanical efficiency

Summary Errors in measurements of mechanical work, net energy expenditure and mechanical efficiency (ME) were calculated, when subjects performed isolated eccentric or concentric muscle actions and combinations of these actions [stretch-shortening cycle (SSC) exercises] with a special sledge apparatus. The relative error of mechanical work was 6.1%. When estimating the error of energy metabolism from oxygen consumption the error would be about 4% (McArdle et al. 1981). The maximum error of ME was the sum of these two values (10.1%). Obviously the error of ME was less than 5%, because 30 muscle actions were averaged and, in addition, the errors of mechanical work and energy expenditure were not in the same direction every time. It was concluded that mechanical work can be determined accurately when the force is measured as a function of the moved distance of the sledge. Thus calculation of ME can be performed quite reliably in isolated eccentric and concentric exercises. The greatest problems were, however, in the SSC exercises, where the errors were higher, because of the problems of dividing the net energy expenditure into eccentric and concentric phases. Therefore, further developments must be made to minimize the errors in measurement and calculation during SSC-exercise.     

Prestretch potentiation of human skeletal muscle during ballistic movement

The conditions associated prior to and during the transition from prestretch to shortering may have considerable influence on the final performance of muscle. In the present study male subjects of good physical condition performed vertical jumps on the force-platform with and without preliminary counter movement. In the counter movement jump (CMJ) the amplitude of the knee bending, velocity of the prestretch and the force attained at end of prestretch were the primary parameters of interest. In addition the coupling time indicating the transition from the eccentric (prestretch) phase to the concentric phase was recorded from the angular displacement and reaction force curves. In the final calculation the mechanical performance parameters of CMJ were always compared with those of the jumps performed without counter movement. The results indicated in general first that CMJ enhanced the average concentric force and average mechanical power by 423 N (66%) and 1158 W (81%), respectively. This potentiation effect was the higher the higher was the force at end of prestretch (p<0.001). Similarly, the prestretch speed (p<0.001) and short coupling time (p<0.01) were associated with enhanced performance during the concentric phase. The average coupling time was 23 ms. The results are interpreted through changes in the prestretch conditions to modify the acto-myosin cross-bridge formation so that the storage and utilization of elastic energy is associated with high prestretch speed, high eccentric force and short coupling time. The role of the reflex potentiation is also suggested as additional enhancement of the final performance.     

The influence of agonist premotor silence and the stretch-shortening cycle on contractile rate in active skeletal muscle

Summary Agonist premotor silence (PMS), a brief period of relative quiescence in active skeletal muscle prior to phasic activation, was investigated in subjects performing maximal contractions. The frequency of occurrence and potential function of the silent period were examined for elbow flexions and extensions. PMS was evident for movements in both directions, indicating that the mechanism is not primarily limited to extensors as previously hypothesized. Flexions demonstrating PMS exhibited increased velocity and acceleration; however, kinematic facilitation was only evident on trials exhibiting the muscular stretch-shortening cycle (SSC). The SSC was present on trials lacking PMS, demonstrating that biceps and triceps silence are not the sole determinants of preparatory agonist lengthening for elbow flexions and extensions, respectively. Taken together, the data indicate that agonist PMS is a mechanism under apparent central control that acts concomitantly with mechanical factors to potentiate elbow flexor contractions.     

The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises

Summary The mechanical efficiency of the leg extensor musculature of men and women was examined with a special sledge ergometer. The subjects (ten males and ten females) performed (a) pure positive work, (b) pure negative work and (c) a combination of negative and positive work (strech-shortening cycle). The mechanical efficiency of pure positive work was on average 19.8±1.2% for female subjects and 17.4±1.2% for male subjects (t=4.12, P<0.001), although the work intensity was equal in both groups. The mechanical efficiency of pure negative work was slightly lower in women than in men (59.3±14.4% vs 75.6±29.3%). The mechanical efficiency of positive work (₊) in a stretch-shortening cycle exercise was 38.1±6.8% in men and 35.5±6.9% in women. The utilization of prestretch was better for female subjects at low prestretch levels, whereas males showed greater potentiation of elastic energy at higher prestretch levels. Regarding absolute W _el (work due to elasticity) values, male subjects showed greater (P<0.001) values than females (189±44 J vs 115±36 J, respectively). Fundamental differences in neuromuscular functions in men and women might cause the differences in the results obtained.     

Effects of long- and short-term fatiguing stretch-shortening cycle exercises on reflex EMG and force of the tendon-muscle complex

This study examined the fatigue effects of stretch-shortening cycle exercises of different intensity and duration on stretch reflex EMG and mechanical responses of the triceps surae muscle. Twelve subjects performed either a 10-km run (n=6) or short but exhaustive rebound exercise on a sledge apparatus (n=6). Passive reflex tests (mechanically induced ankle dorsiflexions) were examined before, after as well as 2 h, 2 and 7 days after exercise. Mechanical reflex responses were recorded from the ergometer torque signal. An acute contractile failure was observed as large reductions in twitch responses, especially in the sledge subgroup who showed high post-exercise peak blood lactate and an increased EMG/torque ratio. Independently of the exercise, the delayed fatigue analysis revealed strong relationships between the reflex-induced EMG and mechanical changes. In addition to muscle damage, these results may be explained by inhibitory effects via the sensitisation of small muscle afferents particularly during the exercise-induced delayed recovery process.     

Combined effect of elastic energy and myoelectrical potentiation during stretch-shortening cycle exercise

In addition to the utilization of muscle's elastic energy enhancement of performance in exercise involving stretch-shortening cycle might be also due to simultaneous increase of myoelectrical activity. This hypothesis was tested by examining three athletes during jumping exercise on force-platform. Vertical jumps were performed with and without preliminary counter-movement, and the jumps were called counter-movement jump (CMJ) and squatting jump (SJ), respectively. In both conditions several jumps were performed also with extra loads on the shoulders (15–220% of b. wt.). Additional droppingjumps (DJ) were executed from different heights (20–100 cm). During jumping exercise myoelectrical activity of selected muscles from the quadriceps femoris was monitored with surface electrodes. The results obtained were similar to those reported in isolated muscle and as expected, the prestretch in CMJ shifted the force-velocity curve of concentric work to the right. In two cases enhancement of performance was attributed primarily to restitution of elastic energy because myoelectrical activity was similar to that observed in SJ. In one subject increased myoelectrical activity was observed during the concentric phase of CMJ. In DJ condition the EMG activity during eccentric phase was much higher than in SJ. Therefore the high performance in this condition was attributed to both elastic energy and reflex potentiation. In eccentric work of CMJ the average force decreased with the increase of stretching speed. This phenomenon was associated with a light increase of EMG activity. The observed results emphasize that both elastic energy and reflex potentiation may operate effectively during stretch-shortening cycle activity.     

Contraction-specific differences in maximal muscle power during stretch-shortening cycle movements in elderly males and females

Elderly people (age 75 years; n=48 males and 34 females) were studied in order to elucidate gender differences in elderly subjects on the determinants of muscle power (force and velocity) during a stretch-shortening cycle. All subjects performed three maximal counter-movement vertical jumps using both legs, on a force platform (Kistler 9281 B). The eccentric (Ep) and concentric (Cp) phases of the jumps were analyzed. The Ep was further divided into an acceleration phase (Ep_acc: from the start of the downward movement to the maximal negative velocity) and deceleration phase (Ep_dec: from the maximal negative velocity to the end of the downward movement). Jump height for the men was higher than for the women (P < 0.001). During both Ep_acc and Ep_dec no significant differences were observed between males and females in force and power generation. However, the men had a higher peak muscle power during the Cp, which may be explained exclusively by the velocity determinant (P < 0.001). No specific gender-related strategy appeared to influence the motor pattern of the movement. The comparable eccentric force generation of the leg extensors in both genders suggests a similar ability to cope with eccentric muscle actions during everyday activities. In contrast, the marked lower capacity for concentric contractions in women may result in an impaired performance, especially in activities where intense and rapid movements are essential, for example when reversing a forward fall. This may be one reason why elderly women are more prone to falls than are elderly men. Accepted: 19 September 2000     

Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers

Summary Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad · s^–1) and knee extensions (1.57 rad · s^–1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70±17%) than for the knee extensors (56±12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71–72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.     

Mechanical muscular power output and work during ergometer cycling at different work loads and speeds

Summary The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints.     

Stretch shortening cycle fatigue: interactions among joint stiness,reflex, and muscle mechanical performance in the drop jump

The purpose of the present study was to investigate the effect of strenuous stretch-shortening cycle exercise on the relationship between reflex and stiffness regulation during the drop jump. Ten healthy male subjects performed submaximal stretch-shortening cycle exercise on a special sledge apparatus. Exhaustion occurred on average within 3 min. A drop jump test from a 50-cm height was performed immediately before and after the sledge exercise, as well as 2 h, 2 days and 4 days later. The fatigue exercise showed relatively high blood lactate concentrations 12.5 (SD 2.6) mmol·l^–1 and a 2-day delayed increase of serum cretaine kinase concentration. In drop jumps, the short latency M1 component of the vastus lateralis muscle electromyogram (EMG) response showed a continuous decline throughout the entire follow-up period after fatigue (NS), whereas the medium latency EMG component increased 2 days after the postfatigue sessions (P < 0.05). Immediately after the fatigue exercise a positive correlation (P < 0.05) was found between the changes in the short latency EMG response and in the amount of knee joint stiffness during the early post-landing phase of the drop jump. This suggests that the M1 response was closely related to the stiffness changes during the initial braking phase of the drop jump. Increase of creatine kinase concentration on the 2nd day correlated negatively with the changes in the drop jump performance (P < 0.05). Since the short latency EMG component has almost recovered on the 2nd day, impairment of the mechanical function of the muscle might have taken place. In conclusion, exhausting stretch-shortening cycle exercise induced local muscle impairment, which resulted in modulation of the reflex and stiffness interaction in the drop jump as well as compensation by central motor command.     

Store and recoil of elastic energy in slow and fast types of human skeletal muscles

Stretch-shortening cycle refers to the mechanical condition in which store and recoil of elastic energy occur in the skeletal muscle. This leads to a greater work output when compared to a simple shortening contraction. The subjects performed vertical jumps with and without preliminary counter-movement and with small and large knee angular displacement. The results indicated that those subjects who had more fast twitch (FT) fibers benefited more from the stretching phase performed with high speed and short angular displacement. The amounts of elastic energy stored in this phase were 30 and 26 N × kgBW^-1, respectively, for FT and slow twitch (ST) type subjects. The recoil of elastic energy was proportional to the amount of energy storage. In large amplitude jumps where transient period between stretch and shortening is long the both types of subjects demonstrated similar amount of storage of elastic energy (17 and 16 N × kgBW^-1, respectively). However, the re-use of this elastic energy was greater in ST group (24%) as compared to the FT group (17%). The results can be interpreted through differences in sarcomere cross-bridge life times between fast and slow muscle fibers. The slow type muscle may be able to retain the cross-bridge attachment for a longer period of time and therefore it may utilize elastic energy better in a slow type ballistic motion.