The vertical countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ) are among the most widely performed movements to assess lower-limb power (20). Despite the popularity of vertical jumps as a test of lower-limb power, many sports require force to be produced in both the vertical and horizontal planes of movement (5,22,28). As such, it has been suggested that the prognostic value of kinetic and kinematic measures taken from vertical jump movements to actual sporting performance is of limited value (5,22). The use of horizontal, or a combination of vertical and horizontal measures of power, may have greater face validity to sporting performance.
A limited amount of research has been undertaken on the relationship between horizontal jump distance and sprint speed (7,24). Research indicates that measures of horizontal jump distance are reliable and may be equally or more effective at predicting functional sporting movements than vertical jump measures (19,22,24). However, measures such as jump distance do not isolate what kinetic or kinematic aspects contribute to jump performance (10). Cronin and Hansen (7) found significant correlations between both vertical and horizontal force measurements in unilateral horizontal DJ compared with sprint speed over short distances. However, to the best of author's knowledge, no comprehensive study has been undertaken to determine the relationship between kinetic variables such as mean and peak force in other horizontal jump types, for example, CMJ, SJ, and bilateral DJ.
Additionally, sprint performance relies on different physiological factors throughout different phases of a sprint, that is, acceleration at different speeds and maintenance of top speed (20). For example, early acceleration is thought to be heavily dependent on concentric contractile force and the rate of force development (21). Similarly, jumps of different types rely on different physiological characteristics, for example, SJ relying on concentric contractile force and rate of force development (7). As such, different jump types may be used to predict performance characteristic during sprinting. Furthermore, different types of plyometric and jump movements may be included in training programs to improve specific physiological characteristics contributing to sprint performance (27).
Muscle stiffness plays a unique and important role in developing muscular force and determining the capacity of a muscle to produce powerful movements (8,13). Muscle stiffness is the muscles ability to resist change in length when subjected to a force (26). This plays an important role in optimizing dynamic movements, speed, and stability during tasks such as running and jumping (4,8). Additionally, tendons are thought to act as a spring in vivo, and tendon stiffness is also thought to be important in optimizing dynamic performance (15). Significant correlations between tendon stiffness and jump performance have been found (4,15). However, the relationship between muscle and joint stiffness and kinetic and kinematic variables in vertical and horizontal jump movements has received limited research.
Of further interest is muscle architecture and its relation to sprint speed (3). Fascicle length is thought to be proportional to the maximal voluntary contraction of a muscle, and pennation angle is thought to dictate the proportion of force transmitted from a muscular contraction to the tendon (18). Fascicle length has been found to be greater in sprint-trained athletes when compared with distance runners (1), and in young men when compared with elderly men (23). Furthermore, Kumagai et al. (16) found 100-m sprinters with personal best times of 10.00–10.90 seconds to have greater muscle thickness and lesser fascicle pennation angle in several lower-limb testing sights than those with personal best times of 11.00–11.70 seconds. As such, it is clear that a relationship exists between fascicle pennation angle, fascicle length and muscle thickness, and functional performance. However, the relationship between these measures and kinetic and kinematic measures in vertical and horizontal jumps has not yet been explored.
Determining the relationship between not only jump height and distance but the kinetic and kinematic variables that contribute to power production in these jumps would give greater prognostic and diagnostic value for strength and conditioning practitioners. No previous research exists, which determine the relationship of kinetic and kinematic variables in the vertical and horizontal CMJ, DJ, and SJ and functional performance. Therefore, the aim of this study was to determine the relationship between kinetic and kinematic measures in both bilateral and unilateral CMJ, DJ, and SJ in the horizontal and vertical plane of movement and sprints speeds over 5, 10, 20, and 30 m, lower-limb muscle stiffness and fascicle angle, and fascicle length of both the vastus lateralis and gastrocnemius.
Experimental Approach to the Problem
The relationship between kinetic and kinematic measures in various jump types and functional performance measures was determined over 3 testing sessions. The first session included a 30-m sprint test, an assessment of lower-limb stiffness and familiarization of all jump types. Sprint speed and muscle stiffness was measured in a randomized order after the standardized warm-up. The second session required the subject to undergo ultrasound imagery to allow the determination of muscle pennation angle and fascicle length at specific points on the vastus lateralis and gastrocnemius of the dominant leg. The third testing session consisted of 3 horizontal and 3 vertical CMJ, SJ, and DJ in a randomized order. Subjects completed the first and third testing session at the same time of day 7 days apart, whereas the second test session was completed in the morning at a date convenient to the subject within the 7-day-period between the first and third tests.
Seventeen highly trained male rugby union players (age = 20.1 ± 2.3 years; mass = 102.3 ± 13.5 kg; 1RM back squat = 182.5 ± 20.1 kg; sprint speed 5 m = 1.04 ± 0.07 s; 10 m = 1.80 ± 0.12 s; 20 m = 3.12 ± 0.21 s; 30 m = 4.40 ± 0.34 s; muscle stiffness = 24.78 ± 9.70 kN·m−1) competing in Senior Club competition were recruited for this study. The study was approved by the Auckland University of Technology Ethics Committee. Written informed consent was obtained from the subjects before study participation. All athletes were over the age of 18 (age = 18–28 years). Subjects had a minimum training age of 2 years in a structured strength and conditioning program and were familiar with plyometric and explosive jump training and sprinting.
This investigation was conducted during an “unloading” period during the off-season where no structured weightlifting was prescribed. Subjects participated in normal club rugby skills training during the testing period. Subjects were instructed not to participate in strenuous exercise in the 24-hour period leading into training sessions. Within subjects, testing was completed at the same time of day in test sessions 1 and 3 and in the morning for test session 2.
The first testing session consisted of a standardized warm-up, followed by a 30-m sprint speed test and a muscle stiffness assessment. The standardized warm-up consisted of 10 minutes of cycling (at 150 W) on a Cycle Ergometer followed by 5 minutes of prescribed lower-limb dynamic stretches. Stretches consisted of high knee lateral rotation, standing side to side groin stretch, calf pumps, front to back and side to side leg swings, and pronated alternating lower back kick overs performed for 30 seconds. Two sprint tests were measured with timing lights (Swift Performance Technology, Brisbane, Australia) over 30 m with the time to cover 5, 10, 20, and 30 m recorded. Subjects were required to start with their preferred foot on a standardized mark 50 cm in front of the first timing light so that the subject would not cross the first timing light at their start point but would cross it in their first stride. Subjects were instructed to sprint at full speed without slowing until they have passed the last timing light at 30 m. A 3-minute rest period occurred between sprints.
Muscle stiffness testing consisted of 10 consecutive maximal effort bilateral hops completed on a Triaxial Force Plate (Objective Design Limited, Auckland, New Zealand) using the maximal repeated hop protocol outlined by Dalleau et al. (8). This testing method has been shown to be highly related (r = 0.98; p < 0.001) to reference measures of muscle stiffness (8). Subjects were instructed to jump for maximal height while keeping their legs as straight as possible and their hands on their hips. Jump height and contact time (CT) were recorded for each jump from force plate data. Two muscle stiffness tests were performed with 3-minute rest between tests. At least 15-minute rest was required between sprint and muscle stiffness tests.
The second testing session consisted of ultrasound imagery using B-Mode Ultrasound (SSD-500; Aloka Co., Tokyo, Japan) to determine muscle thickness, and fascicle pennation angle of both the vastus lateralis and gastrocnemius. Ultrasound testing was completed by a professional ultrasound practitioner familiar with the use of B-Mode Ultrasound. Ultrasound testing took place in the morning under resting conditions. No attempt was made to standardize hydration levels during ultrasound testing.
Muscle thickness was measured as the distance between the adipose tissue-muscle interface and the muscle-bone interface in vivo and was determined using ultrasonic images (1). The precision of this method has been previously established (14). Fascicle pennation angle was measured by the angle between the deep aponeurosis of the muscle and interspace among the fascicle of the muscle, this method for determining pennation angle has been used in previous research (1). The vastus lateralis measure were taken midway between the lateral condyle of the femur and the greater trochanter with the subject lying supine, whereas the gastrocnemius measure were taken at 30% proximal between the lateral malleolus of the fibula and the lateral condyle of the tibia with the subject lying prone (1). Each measure was determined by taking the average of 3 trials. These measures have been previously shown to be highly reliable (17,25).
The third testing session consisted of 12 sets of jumps with 2-minute rest between each set. Each set consisted of 3 repetitions with 30-seocond rest between repetitions. The jumps (CMJ, SJ, and DJ) were performed as unilateral vertical, bilateral vertical, unilateral horizontal, and bilateral horizontal and completed in random order. Unilateral jumps were performed using the subjects' dominant leg. Data for jump tests were collected using a Triaxial Force Plate (Objective Design Limited, Auckland, New Zealand) at a sampling rate of 500 Hz. Vertical force, velocity and impulse, and horizontal force were recorded and stored for subsequent analysis using a custom-designed software program (Objective Design Limited, Auckland, New Zealand).
Both vertical and horizontal CMJ consisted of a self-selected countermovement depth immediately followed by a jump of maximal intensity (22). Instructions were given to jump for maximal height or distance in vertical and horizontal CMJ, respectively. Assessment of SJ consisted of a 3-second static hold at an approximate 90° knee angle followed by a jump of maximal intensity in either the vertical or horizontal plane of movement (6). No additional eccentric dip was allowed after the static hold. Any eccentric dip immediately preceding concentric movement resulted in that test being disqualified and repeated after a 30-second rest. Assessments of DJ were performed with a drop depth of 20 cm in unilateral DJ and 40 cm in bilateral DJ (20). This was immediately followed by a jump of maximal intensity. Subjects were instructed to minimize CT on the force plate while maximizing jump height or distance.
In an attempt to standardize testing conditions, minimal feedback was given to subjects during all testing sessions; however, feedback was given to correct technical errors in testing, for example, concentric dip in SJ. Reliability of jump tests for all kinetic and kinematic jump measures and performance tests used in this research was determined before testing. Reliability of the different tests ranged from intraclass correlation coefficient of variation: 0.71–0.97 and coefficient of variation: 2.1 to 9.9%.
The mean and SD of all measured variables were calculated. Mean and peak force measures were divided by subjects' weight to give a measure of relative force, absolute force was used in correlation analysis. Pearson's product-moment correlation coefficient were used to determine the strength of the relationships between vertical and horizontal kinetic and kinematic variable (mean force, peak force, CT, mean velocity, peak velocity, time to peak velocity, mean impulse, and peak impulse) and measures of sprint speed, muscle stiffness, and muscle architecture. The magnitudes of the correlation coefficients were interpreted as: <0.10 = trivial, 0.10–0.29 = small, 0.30–0.49 = moderate, 0.50–0.69 = large, >0.70–0.89 = very large, >0.90 = nearly perfect (11). Coefficient of determination (R2) was also calculated.
The summary of the results for the jump tests is shown in Table 1. Measures of horizontal peak and mean force, in both bilateral and unilateral jumps, had greater relationships to sprint speeds (R2 = 0.132–0.576) than peak and mean force in the vertical plane (R2 = 0.008–0.504), with the exception of mean force in the bilateral SJ (horizontal R2 = 0.371–0.465, vertical R2 = 0.412–0.504). In bilateral jumps (Table 2), mean and peak force measures in horizontal CMJ and DJ have larger correlations to sprint speed over 10, 20, and 30 m then vertical CMJ and DJ. However, in bilateral SJ, mean and peak force in both vertical and horizontal jumps show similar, generally large, correlations to sprint speeds. In unilateral jumps (Table 3), mean and peak forces in horizontal jumps were found to have larger correlations to sprint speed over all distances than vertical jumps of the same type.
Few of the jumps showed large correlations between force measures and 5-m sprint speed. In vertical jumps, only mean force in the bilateral SJ showed a large correlation to 5-m sprint speed. Although horizontal jumps showed more large correlations to 5-m sprint speed than vertical jumps, fewer large correlations were found to sprint speed over 5 m than over 10, 20, or 30 m. No large correlations were found between CT and sprint speed. However, CT generally had greater correlation to 5 m sprint speed than sprint speed over longer distances.
Vertical velocity variables showed some of the strongest correlations to sprint speed out of all tested variables (Tables 4 and 5). Unilateral measures of velocity tended to have larger correlations to sprint performance than their bilateral counterparts across all jump types. Additionally, peak and mean velocity in SJ showed larger correlations to sprint speed (bilateral R2 = 0.228–0.635; unilateral R2 = 0.393–0.574) than CMJ or DJ. Correlations between time to (TT) peak velocity and sprint speeds were also largest in unilateral and bilateral SJ as compared with CMJ and DJ.
No measured variables showed large positive correlations to muscle stiffness. However, mean and peak forces in both bilateral and unilateral horizontal SJ were shown to have large negative correlations to muscle stiffness. Mean force in the horizontal unilateral CMJ and vertical unilateral CMJ were also found to have large negative correlations to muscle stiffness (horizontal R2 = 0.256, vertical R2 = 0.408). In the unilateral CMJ, a large correlation between peak velocity and muscle stiffness was also found (R2 = 0.410).
Similarly, few measures variables showed strong correlations to measures of muscle architecture. Fascicle angle in both the lateral gastrocnemius and vastus lateralis showed no large correlations to force measures for any jump type. However, in the bilateral SJ, fascicle angle of the vastus lateralis showed a large correlation (R2 = 0.292) to peak velocity and fascicle angle of the lateral gastrocnemius showed a large correlation (R2 = 0.279) to TT peak velocity. Fascicle angle of the vastus lateralis also showed large correlations to mean velocity (R2 = 0.296) and mean impulse (R2 = 0.360) in the unilateral CMJ. Muscle thickness of the lateral gastrocnemius had large correlations to peak force in the bilateral DJ (R2 = 0.430) and SJ (R2 = 0.254) vastus lateralis had a large correlation (R2 = 0.298) to peak velocity in the bilateral CMJ.
The purpose of this study was to determine the relationship between kinetic and kinematic measures in bilateral and unilateral CMJ, DJ, and SJ in the horizontal and vertical plane of movement and measures of functional performance. The results indicated that horizontal mean and peak force have a better relationship to sprint performance than vertical mean and peak force. Historically, measures of muscular explosive ability have predominantly been undertaken in the vertical plane of movement. In light of the current research, it would seem that horizontal mean and peak force are useful prognostic measures for many functional movements, such as sprint speed, and should be included alongside their vertical counterparts. This could provide strength and conditioning practitioners with useful information about the physical qualities of their athletes, which is not fully captured by relying on vertical measures alone. These findings are consistent with previous research, which has shown horizontal jump for distance to have stronger correlations to sprint speed than vertical jump height (19,22).
Additionally, many kinetic and kinematic variables measured in horizontal jumps had stronger correlations to sprint performance than the same measures taken in vertical jumps. These findings suggest that using horizontal dynamic training movements may have a greater transfer to sprint performance than vertical dynamic training. Particularly, it would seem reasonable to favor those jump types shown to have stronger correlations to sprint performance, for example, unilateral DJ and SJ. Further training studies are required to prove this hypothesis.
The majority of human movements, including sporting movements, involve some degree of unilateral force production (22,28). As such, it has been suggested that unilateral assessments are more closely related to functional movement than bilateral assessment and therefore may provide better training information (19,22). The current research largely supports this claim, as the kinetic and kinematic measures from unilateral jumps generally had a stronger relationship to sprint speed in both the vertical and horizontal CMJ and DJ. However, this was not the case for the SJ, which showed similar correlations between unilateral and bilateral force measures and sprint speed in horizontal jumps and greater correlations in vertical jumps.
Mean and peak velocity in the vertical CMJ and SJ were shown in this study to have strong correlations to sprint performance. However, horizontal velocity was unable to be determined in this research. This research shows that kinetic variables in horizontal jumps seem to have stronger relationships to sprinting speed than in vertical jumps. As such, it would seem that horizontal velocity may be a promising predictor of sprint performance. Further research should be undertaken into the relationship between horizontal velocity and functional performance measures and use longitudinal designs to investigate this question more fully.
Additionally, it has been previously suggested that different jump types rely on mechanisms in vivo, which relate to physiological factors important throughout different phases of a sprint and that both the DJ and sprint performance at high speed depend heavily on the elastic property of muscles and tendons in the stretch shorten cycle (20,32). Thus, DJ ought to have a stronger relationship to sprint speed over longer distances. The current research clearly supports such findings with peak and mean force and velocity having progressively stronger correlations to sprint speed over greater distances. This also supports the concept that training the stretch shorten cycle through DJ movements may improve acceleration at high speed and speed maintenance.
The SJ is thought to isolate the physiological characteristics, which are important to early acceleration during a sprint movement, that is, concentric contractile force and the rate of force development (21,32). Previous research supports this by demonstrating stronger relationships between concentric force in vertical SJ performance and sprint speed over short distances than longer distances (32). This is somewhat supported by the findings of this article, which has found force and velocity measures in the SJ tended to have greater correlations to sprint performance over shorter distances. However, this is not the case in the horizontal SJ, which shows both stronger correlations than its vertical counterparts and correlations, which were generally as strong or stronger over longer distances, that is, 20–30 m. This suggests that horizontal SJ may be an effective tool in developing both early acceleration but also physiological characteristics relevant to sprint speed over longer distances. Further research is required in this field.
Muscle stiffness was shown to largely have trivial or small negative correlations to both unilateral and bilateral jump kinetic and kinematic measures. Although this is counterintuitive, particularly when comparing muscle stiffness to DJ variables, this is not the only research to produce such findings. Walshe and Wilson (29) found stiff subjects performed less well than their compliant counterparts in vertical CMJ and DJ height tests. However, additional research has shown positive relationships between vastus lateralis aponeurosis tendon stiffness and dynamic performance including SJ and CMJ height (4) and series elastic component stiffness and concentric motion in the bench press (31). Additionally, male adults have been shown to have greater muscle leg stiffness than female adults during volleyball block jump landing (12) and male children during CMJ (30). Although it seems clear that a relationship exists between running economy (9), the relationship between muscle stiffness and jump performance seems unclear.
Tendon stiffness is also thought to be important in important in optimizing dynamic performance (15) and has been shown to have a significant correlations jump performance (4,15). However, tendon stiffness was not measured in this study. Understanding how this variable affects the kinetics and kinematics of jump performance would be of interest.
Previously, measures of muscle architecture have been shown to have significant correlations to sprint performance (2,16,23). In this study, there were no very large correlations between kinetic and kinematic variables in horizontal and vertical jumps. However, several large positive correlations were found between muscle thickness and fascicle angle of the vastus lateralis and velocity and impulse measures in CMJ and SJ. The lack of very large correlations may be a result of differences in subject populations between this study and previous research, that is, sprint-trained athletes (2,16) as compared with rugby players in this study. Furthermore, Blazevich et al. (3) showed that although subjects who participate in strength training to the exclusion of sprint training show improvements in measures of muscle architecture, they show no improvement in sprint speed. Position-specific training variation is common in high-performance rugby players. As such, it is possible that a highly trained forward may have improved measures of muscle architecture through strength training without improving dynamic ability, whereas a back may have both improved dynamic ability and measures of muscle architecture through dynamic jump and sprint training. Regardless, this research shows some vertical and horizontal jump kinetics and kinematics have meaningful relationships to muscle architecture in this group of subjects. Further research into the relationship between measures of muscle architecture, jump kinetics and kinematics, and functional performance measures in more diverse population groups would be of interest.
The present findings suggest that strength and conditioning practitioners concerned with the prognostic value of kinetic variables to functional movements such as sprint speed should also use horizontal jumps alongside vertical jumps in testing and training. Peak and mean force in the unilateral DJ, mean force in the bilateral DJ, and mean force in both the vertical and horizontal bilateral SJ showed the strongest relationship to sprint speed. Furthermore, peak and mean force in horizontal CMJ had greater correlations to sprint speed than in the vertical CMJ. As these horizontal jump movements have large correlations to sprint speed, it is also likely that using horizontal dynamic training movements, particularly those jump types shown to have stronger correlations to sprint performance, may have a greater transfer to sprint performance than vertical dynamic training. Furthermore, mean and peak velocity in bilateral and unilateral SJ were found to have a strong relationship to sprint speeds, jumps of this modality focusing on velocity of movement should be favored as a training tool for sprint speed.
Additionally, this study supports previous research, which has suggested that DJ movements have stronger relationships to sprint speed over longer distances. This is true in both the vertical and horizontal DJ. As such, practitioners can use this jump type to improve acceleration at high speed and speed maintenance. However, horizontal SJ did not have greater correlations to sprint speed over shorter distances. It seems, therefore, that this may not be used by practitioners to target concentric force production specifically although considering the strength of the correlations to all sprint distances, this jump modality would still seem to be effective as a training tool to improve sprint performance.
The authors thank the athletes who participated in this study and the Waikato Rugby Union for their support of this study. There exists no conflict of interest for any of the authors of this study.
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