McKenzie, Chloe PG Dip; Brughelli, Matt PhD; Gamble, Paul PhD; Whatman, Chris PhD
Researchers have suggested that holding loads in each hand during a standing horizontal jump can affect the mechanics of a jump and consequently improve jump performance (1,4,17). This concept dates back to ancient Greece when the standing long jump was performed at the Olympic Games nearly 3,000 years ago (∼700 B.C.) (1,4). Ancient sources reported that athletes jumped more than 15 m with loads in their hands during a continuous succession of 5 broad jumps (17). According to legend, ancient athlete Phayllos jumped 55 feet (17). Interestingly, pictographs illustrate ancient athletes carrying load in their hands while performing various maneuvers. The stone or lead loads ranged from 2 to 9 kg and were shaped in a primitive form of a dumbbell (4,18). Handheld load may therefore be one of the earliest tools invented to passively enhance human athletic performance. Even though the standing long jump has been excluded from the Olympic Games since 1912, it continues to be a popular test of explosive leg power in field testing today (23).
Given the importance of maximizing horizontal jump distance in many different sport activities, jumping with loads has been seen as a valuable training mode to investigate (1,15). Based on the acute enhancement of jump distance with handheld loads, the training effects of enhanced jump performance, when loaded horizontal jumping is repeatedly applied, may prove to be useful in many sports and sporting activities. Long jump is clearly an example of a sport that could benefit from such training; however, in other sports such as volleyball and basketball, athletes need to produce a certain amount of horizontal momentum in addition to jumping vertically to be able to achieve successful performance (19).
The purpose of this review is to attempt to verify the historical veracity of the effect of handheld loads on jumping (both vertical and horizontal) mechanics and performance and provide practical recommendations for future research and training. In addition, the 4 main theories of arm motion mechanics will be used to help explain why jumping may be enhanced with handheld loads.
The effects of arm motion (i.e., arm swing) during both vertical and horizontal jumping have been investigated by several researchers. Performing jumps with free arm motion has been shown to increase jump distance and/or jump height, compared with jumping with the restriction of free arm motion (2,3,5–9,11–13,16,23). Improved jump performance can be explained by an increase in the height or distance of the center of mass (CM) at takeoff (TO) and an increase in velocity of the CM at TO (5,7,8,16). The underlying mechanisms for such results can be partly attributed to 4 main theories, which affect the mechanics and motion of the body during a jump: pull theory, joint torque augmentation theory, hold back theory, and TO angle theory. The same theories have been proposed for the augmentation in jump performance with handheld loading.
During a vertical or horizontal jump with an arm swing, the work created by the muscles at the shoulder and elbow joints imparts energy, transferring it to the rest of the system (2). The transfer of energy from the shoulders and elbows is termed “pull theory.” Arm swing begins to decelerate near TO during the end propulsive phase of a jump, causing the torque at the shoulder joint to pull the trunk up (in a vertical jump) or forward (in a horizontal jump) (5). This causes energy to be transferred from the arms to the rest of the body, increasing jump performance (2,5,16). Work reported at the shoulder joint was fairly similar in the studies by Lees et al. (16) and Domire and Challis (6) and was shown to contribute to approximately 33% of performance enhancement (6). These results were slightly lower than the findings in a simulation study by Cheng et al. (5) who reported that shoulder joint work was responsible for approximately half (52%) of additional energy caused by arm motion. Cheng et al. (5) also found the arms to pull the body up for a shorter time than that measured by Lees et al. (16). These inconsistent findings are most likely because of methodological differences. One study used human participants (6) and the other computer modeling (5).
JOINT TORQUE AUGMENTATION THEORY
An increase in jump height with an arm swing has also been associated with “joint torque augmentation” (5–8,12). Swinging the arms during the early propulsive phase of a jump generates a downward force at the shoulder, which is transferred to the trunk and the rest of the body (2). This downward force slows the shortening of the major lower body muscles when they are in an optimum position to produce force (8). Additionally, a decrease in shortening velocity allows the relevant muscles to produce more force according to the force-velocity relationship (2,6,12). Feltner et al. (7) reported a decrease in torques at the hips, knees, and ankles during the early propulsive phase of a jump but augmented later in the propulsive phase, referred to as joint torque augmentation. Torques at the hip and ankle were also reported to be significantly augmented with arm swing by Hara et al. (12), contributing 66% of work from the lower extremity joints toward the total increase in overall joint work. Hip joint torque was also found to considerably increase (47%) in the study by Cheng et al. (5) when the use of free arm motion was compared with no arm motion (163 versus 240 Nm). However, joint torque augmentation was confirmed only in the hips and not the knees (joint work 7% less with arm motion) and ankles (joint work 18% less with arm motion). As a direct consequence of hip joint torque augmentation, ground reaction forces (GRF) increased in the latter half of the propulsive phase of a jump (5,13).
HOLD BACK THEORY
Ashby and Heegaard (3) investigated horizontal jumps with and without free arm motion to determine if arm swing improved jump distance. The results of this study showed that the subjects jumped an average of 21% further with free arm motion than without. A 13% increase in TO velocity when free arm motion was allowed accounted for the majority of the increase in performance, whereas the remaining increase was because of an increase in the horizontal displacement of the CM before TO. Jumping with restricted arm motion was found to cause a decline in the vertical GRF just before TO resulting in a backward rotation moment about the CM (3). It has been suggested that without the ability to swing the arms, the jumper must overcome excessive forward rotation that would prevent correct landing. To do so, the jumper must “hold back” or limit lower limb extensor activation during the propulsive phase, hence the “hold back theory” (2). Thus, for a successful jump, the additional balance and control provided by free arm motion (ability to swing the arms backward during flight phase) are necessary to correct excessive forward rotation about the CM (3).
TAKEOFF ANGLE THEORY
The direction of arm swing and TO projection angles are also indicators of horizontal jump performance (11,23). Velocity of the CM at TO has been shown to decrease with an increase in TO angle and thus negatively affect flight time and performance during the long jump. The optimum TO angle was determined to be 19–27° (23), much lower than the expected optimum angle for projectile motion of 45°. It is only when the magnitude of the projection velocity of a jumper is the same for all projection angles that the projection angle of 45° is optimal (23). As the projection velocity is known to decrease as the projection angle increases in long jumpers, the 45° projection angle is not optimal. Thus, identifying methods of increasing the projection angle at TO (above the found optimum TO angle of 19–27°) while still maintaining TO velocity would seem to augment horizontal jump performance.
THE EFFECTS OF HANDHELD LOADING ON PERFORMANCE
The technique of the ancient Greek long jump has been investigated to determine the credibility of the athletic achievements described in ancient sources. It has been suggested that the most likely explanation of the great feats of the ancient Greek long jump is a jump comprising a continuous succession of 5 jumps (5-fold jump) where the athlete was able to gain balance and momentum between each jump. Lenoir et al. (17) investigated the effects of handheld loading and reported a 5–6% average increase in jump distance. Therefore, the 5-fold jump technique suggests that trained athletes are able to jump distances over 15 m, indicating that the jump of Phayllos is an acceptable possibility (17).
Researchers have also found positive increases in horizontal jumping distance using a single standing long jump (4,15,20–22) or a vertical jump approach (18) (Table). An increase in jump distance was recorded by Tang and Huang (22) who found that an unloaded jump distance of 2.68 m increased to 2.82 m (P < 0.05) with a 6–8 kg handheld load. Butcher and Bertram (4) reported that the biggest increase in jump distance was found between an unloaded jump and a jump with a handheld load of 7.2 kg. Minetti and Ardigo (18) showed increases in jump performance of 5–7% using handheld load in the mass range of 2–9 kg. However, this study involved vertical jumping, and therefore, improvements in horizontal distance can only be estimated (at least 17 cm during a 3-m jump).
Table-a Effects of h...Image Tools
The optimal loading range where horizontal jump distance is maximized has also been investigated. The sequential increase of load in the designs of several studies has allowed this to be investigated (15,20,21). Common loading between studies consisted of no extra load, light load (2–4 kg), heavy load (6–8 kg), and super heavy load (10–12 kg) (15,21,22). Tang and Huang (21) found that the optimal load to enhance jump distance was approximately 5% of the participant's body mass. This was in accordance with Huang et al. (15) who found that the optimal load to enhance jump distance was 6% of the participant's body mass (approximately 4.24 kg). The loading range used by Filush (9) was based on 6% of body mass as determined by Huang et al. (15). Jump distance in this study increased from 2.41 m (no loading) to 2.50 m (P = 0.004), supporting that 6% of body mass loading has positive effects on performance (9). Despite Papadopoulos et al. (20) using slightly different loads (no load, 3 kg, and 6 kg) compared with Tang and Huang (21) and Huang et al. (15), the results are consistently identifying an optimal load of 4–8 kg. A slightly higher optimal load of 8% of body mass has also been identified in the literature (4,14). Collectively, these findings indicate that ∼5 to 8% of body mass is the optimal load for an enhanced jump distance of ∼9 to 15 cm. It should be noted that the ∼5 to 8% of body mass is a combined load for both hands. In other words, ∼2.5 to 4% of body mass for each hand could be considered optimum. Minetti and Ardigo (18) also observed a decline in performance when handheld load exceeded 10–12 kg. Similar findings suggest that jump performance is negatively affected once load exceeds the optimum (4,22).
Table-b Effects of h...Image Tools
Computer simulation studies have also shown that handheld load can increase jump performance (1,18). Two computer simulations have been conducted with the use of a 2-dimensional software model of a long jumper; one created from 4 body segments (18) and the other from 7 body segments (1). The horizontal jump distance improved in both studies; however, the extent of improvement was not consistent. An improvement in performance of 39 cm was found by Ashby (1), compared with a smaller improvement of 17 cm found by Minetti and Ardigo (18). The reason for this finding is most likely because of the differences in jump methods between studies. Minetti and Ardigo (18) measured vertical jump distance, and Ashby (1) measured horizontal jump distance. Other reasons could involve the different number of body segments analyzed when measuring the jumps and the different loads applied (0–20 and 4–12 kg, respectively). In addition, simulation results by Ashby (1) determined 8 kg to be the optimum load to enhance jump distance, which is slightly higher than the values produced by studies involving human participants (15,20,21). In comparison, optimal loads as determined by Minetti and Ardigo (18) were similar to those suggested by the studies involving human participants.
THE EFFECT OF HANDHELD LOADING ON JUMP KINEMATICS
The ability to perform effectively in many sports, such as basketball and volleyball, requires a certain amount of horizontal momentum (mass × velocity) (19). Therefore, when investigating the effects of handheld load on horizontal jumping to determine jump performance, it may be useful to measure horizontal force, jump duration, and ultimately horizontal impulse. These measures have been considered in previous studies using force plates (14,15,18,20–22). The use of handheld load results in greater peak horizontal forces (14,15,18,21,22) with a strong, positive correlation found between jump performance and peak horizontal force (r = 0.85, P = 0.007) (20). Tang and Huang (22) found an increase in peak horizontal force from 736.5 N with no load compared with 821.3 N with a heavy load. Increases in jump duration and horizontal impulse have also been reported with handheld loading (15). Huang et al. (14) and Tang et al. (21) suggested that the improvements in jump distance were most likely because of the increases in horizontal impulse.
LIMITATIONS OF PREVIOUS LITERATURE
All the studies reviewed on the effects of handheld load on performance in the standing long jump have come from conference abstracts (1,14,15,22), case series designs (17,18,20,21), a university publication (4), and a Master's thesis (9). Currently, there are no studies published in this area in an international peer-reviewed journal. Furthermore, these studies have included low participant numbers, homogeneous participants, simulation studies, inadequate familiarization, and limited reporting of reliability. Additionally, all the reviewed studies have used predominantly male participants. Therefore, further studies are needed involving female participants and addressing the methodological issues noted above.
Although the evidence for the effectiveness of handheld load on jump performance is currently limited, there are several possible practical applications. One application of handheld loading is as a coaching aid to help develop jumping technique. Arm swing has been shown to be a key contributor to vertical jump performance, and individuals do vary in their ability to use the arm swing action effectively to optimize jump performance. In this context, handheld loading allows the individual to focus and refine their arm swing technique, which is likely to improve their (unloaded) vertical jump scores. In sports where vertical and standing long jump measures are employed for talent identification and selection (a notable example being the American National Football League combine), maximizing an athlete's height or distance scores on the particular jump assessment is a goal in itself. A complex training approach might be adopted for this purpose, alternating handheld loaded jumps and unloaded jumps with arm swing. Indeed, this may help to reinforce technique while avoiding any potential disruption in timing for the unloaded jump movement.
Alternatively, a handheld loading exercise may be employed solely as a potentiation exercise to increase neural drive and power output for another activity. In this manner, handheld loaded jumps might be performed before sets with heavy speed-strength training modes, such as barbell jump squats and Olympic-style lifts. Similarly, handheld loaded jumps might be used as a primer for maximal acceleration efforts (e.g., sprint start), sprint bouts, or even throwing efforts.
The other major application of handheld loading is as a training tool (Figure). Authors previously identified that a major limitation of the majority of conventional strength and power-oriented exercise modes is that they have a vertical bias, and as such, there is a need for training modes that provide the development of horizontal GRF production (10,24). Mainly, the standard “horizontal” speed-strength exercise options available to the practitioner involve only body weight resistance. For example, the horizontal speed-strength training modes most commonly employed comprise (body weight) plyometric training exercises in a horizontal direction. Handheld loading offers a means to add external resistance for these horizontal speed-strength and plyometric exercises that involve arm swing.
Figure. The standing...Image Tools
From this viewpoint, in addition to single-jump efforts with countermovement, handheld loading might also be considered for drop jumps in vertical and horizontal directions. Similarly, handheld loading has been successfully employed with repeated jumps. Other possible applications include vertical jumps performed with a run up, with options for either single- or double-leg TO.
Handheld loaded repeated jumps for height performed in a forward direction similarly offer an alternative to jumps performed in series onto and off boxes or jumps over hurdles. Stair bounds with handheld loading is another option available to the practitioner. Stiff-legged bounds (performed with abbreviated arm swing) similarly offer a means to provide lower leg conditioning with augmented eccentric loading.
There are also a number of modifications and progressions available for handheld loading. These include single-leg variations for the various vertical and horizontal jump modes described. Single-leg, single and repeated jumps with handheld loading might also offer a means to identify and correct differences in function and performance between limbs.
Despite methodological concerns highlighted in this article, results found in the reviewed studies support the use of handheld loading to improve jump performance. Four main theories of arm motion were used to explain possible increases in jump performance with handheld loads. A 5-fold jump was identified as being a likely explanation of the great feats of the ancient Greek long jump, in particular the recorded jump of Phayllos. Practical applications to implement the use of handheld loading involve eccentric preloading or potentiation exercises during training and using handheld loading as an aid to help develop jump technique, all of which can be modified and progressed. Furthermore, well-designed studies are needed to investigate the effects of handheld loading on jumping biomechanics and performance of female athletes. Future studies should also focus on determining appropriate training protocols for performance enhancement.
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