Relative PP was greatest in the assisted jump and was 35.0% (±22.7%) greater than the resisted jump (very large ES). Additionally PP (W·kg−1) was 34.0% (±13.7%) greater in the free than in the resisted jump (very large ES). There was no difference in relative PP between the free and assisted jump conditions (Table 3). Figure 5 illustrates the variation in velocity, PP, and peak force, in the separate countermovement jumps between subjects.
The amplitude of force unloading during the early unloading phase (phase A) of the jump was 16.9% (±17.1%) greater in the resisted jump than in the assisted jump (moderate ES) (Table 4). There was no difference in the rate of force unloading during the early unloading phase.
The peak force produced during the loading phase (phase B) was 5.8% (±6.4%) and 17.2% (±5.8%) greater in the resisted jump than in the free and assisted jumps (small and moderate ES, respectively). Additionally peak force was 10.7% (±4.0%) greater in the free jump compared to in the assisted jump (small ES). A small difference was observed in the change in force during the loading phase and was 7.9% (±11.5%) greater in the resisted jump when compared to in the assisted jump method.
The rate of force development, measured as the slope of the force-time curve in the loading phase (phase B), was greatest in the resisted jump (4,268 ± 2,125 N·ms−1 ). A moderate difference of 21.6% (±26.5%; 90% CL) was observed in the rate of force development during the loading phase between the resisted jump and free jumps.
The rate of force decline, calculated as the (negative) slope of the force-time curve from peak force to zero force (phase C) was greatest in the resisted jump when compared to in free (19.5 ± 22.5%; 90% CL) and assisted jumps (78.2 ± 75.7%; 90% CL) and represented a small and moderate ES, respectively.
The greatest impact force was generated in the resisted jump (phase D) and was 66.5% (±41.3%; 90% CL) and 22.0% (±25.0%; 90% CL) greater than in the assisted jump and resisted jump, respectively (ES, moderate). Additionally, the free jump produced 36.4% (±35.3%; 90% CL) greater force on impact when compared to the assisted jump (ES, moderate). Similarly, the greatest rate of force development on impact was generated in the resisted jump, being 98.7% (±45.8%; 90% CL) and 35.7% (±33.4%; 90% CL) greater than the assisted jump and free jump (ES, moderate and small, respectively). Additionally, the rate of force development on impact was 46.4% (±39.8%; 90% CL) greater in the free jump when compared to the assisted jump (ES, moderate).
The analysis revealed that both assisted and resisted jump training groups had a small increase in jump height of 6.7% (±9.6%) and 4.0% (± 8.8%), respectively, whereas the free jump group produced a trivial increase in jump height of 1.3% (± 9.2%). A small effect was observed for the between-group difference in the change in jump height between assisted and free jump training (5.6, 90% CL ±6.8%), and resisted and free jump training (3.7 ± 6.1%). Trivial but unclear between-group differences were observed in the change in jump height between the assisted and resisted jump training protocols. Figure 6 illustrates the variation in vertical jump height change of each subject in the 3 separate conditions.
The purpose of part 1 was to examine the differences in the kinetics of assisted, resisted, and free countermovement jumps. The findings were then used to help plan and implement the training protocols in part 2, which examined the differences in training effect of these training methods.
As expected from the concentric force-velocity relationship, the greatest peak velocity was achieved during the assisted jump because the vertical assistance provided by the elastic bands reduced the effective bodyweight of the subject by providing an upward propulsive force. The assisted jump therefore allowed subjects to jump more quickly than is possible without assistance. Previous literature has shown increased neural activation (via integrated electromyography) when performing at supramaximal velocities (29) that may have positive training implications. The greatest PP relative to bodyweight was also achieved in the assisted jump condition, with this effect likely because of the increased velocity of the movement. Assisted training may be particularly beneficial for athletes who have already obtained high levels of strength, but lack the ability to produce higher power outputs or movement velocity, especially at low loads.
There was a reduced amplitude of force unloading in the early unloading phase of the assisted jump in comparison to resisted and free jumps, and may have reflected in some ways a decreased stretch-shortening cycle force contribution. Reductions in force unloading and rate of unloading may have resulted in less stretch on the muscle-tendon complex, and therefore, the tendon would have recoiled with reduced force (24). As such, the total force produced during the assisted jump would have had a greater reliance on concentric-only muscle force production, which may help to explain the smaller change in force compared to the resisted jump during the loading phase (24).
The assisted jump was associated with substantially smaller impact forces than both resisted and free jumps. In a training environment, the reduced impact forces observed during assisted jumps may be a safer way to graduate the intensity of plyometric loading, especially after recovery from lower-body injury or in large athletes who may not tolerate high landing ground reaction force.
Maximum force, rate of force development, and impact force were greatest in the resisted jump condition. The observation that the resisted jump condition allowed the greatest peak force is likely because of the increased resistance reducing movement velocity. Indeed, according to the force-velocity relationship, force is greater at slower concentric contraction speeds and reduces as the velocity of the concentric action increases (19). In contrast to assisted jumping, the greater force and rate of force development produced in the resisted jumps may have been because of the larger force unloading in the early unloading phase of the jump. Greater unloading forces and rate of force unloading during this phase may have increased tendon recoil thus enhancing stretch-shortening cycle function. Indeed Kubo et al. reported that a faster prestretch of human muscle led to greater muscle-tendon complex lengthening with 22.3% greater work completed in the following concentric action than at a slower prestretch rate (24).
It is well known that power production during complex movement is influenced by many different factors (e.g., force, velocity, rate of force development, stretch-shortening cycle efficiency) (30). Part 1 of this investigation determined that both assisted and resisted jump methods produced distinct maximal outputs, which may be expected to develop different components of muscular power (high speed and low force, low speed and high force, respectively). The free jump did not result in a greater output than the assisted or resisted jumps in any of the measured variables.
There are some limitations that should be considered before attempting to interpret the results from part 2 of this investigation. Firstly, the assistance and resistance provided varied between participants and was not assessed on every set of every training session; and secondly, the competition game performed by the subjects could not be completely controlled in terms of the specific role each athlete played within the match, tasks completed or time on the field.
Results of part 2 indicated that assisted and resisted jump training led to small improvements (4.0-6.7%) in vertical jump height in well-trained rugby players during the competitive phase of their season. In contrast, trivial improvements (1.3 ± 9.2%) in jump height were observed after free countermovement jump training. These findings are important considering prior research from this group indicating a 3.3% decrease in lower-body power in similar well-trained rugby players over a competitive season (2). It is also important to note that in similar well-trained athletes Baker and Newton (5) reported 5% improvements in power over a 4-year training period, as such, trivial performance improvements may still be important. If 4.0-6.7% improvements in jump height can be achieved with assisted or resisted jump training over a 4-week training period with minimal disturbance to training, without the risk of injury and at minimal cost, then coaches should confidently employ such training methods. Furthermore it should be restated that these results were obtained where resistance training, speed development, team skills, and training sessions, along with competitive matches were being performed within the same training phase. As such, these findings are likely more transferable to real-world applications compared to what is observed in single training mode or laboratory-based investigations.
Assisted jump training resulted in the greatest increase in vertical jump height and was associated with the greatest acute peak velocity and power outputs. Findings from part 1 revealed that performing assisted jump training allowed participants to jump with a movement velocity greater than in the free and resisted jump conditions. Training at a higher movement speed may have resulted in decreased antagonist coactivation or an increase in Myosin heavy chain-II fiber activation (1). Indeed, there is a close relationship between muscle shortening speeds and the expression of the different (MHC) isoforms (9,25). Additionally, muscle fibers that contain MHC-I have slower maximal shortening velocities and lower power outputs than muscle fibers containing MHC-II isoforms (9,25). Although it was not assessed in this investigation, our results may suggest that the higher velocity training resulted in very specific morphological adaptations. Neuromuscular adaptations should not be discounted as possible mechanisms for the improvements observed in jump height. Indeed, Newton et al. (32) reported that greater velocity and force production (as observed in assisted and resisted jumps, respectively) provides superior loading conditions for the neuromuscular system. As such, the greater stimulus may have promoted positive adaptation (6).
Resisted jump training improved vertical jump height by 4.0% and was associated with the greatest peak force and rate of force development. It is likely that the increased force requirements of resisted jumping led to positive adaptation. Attempting to move at high speeds against a larger external load may induce numerous adaptations including an increase in contractile force, perhaps through increased neural activation, reduced coactivation, and muscle architectural and fiber size adaptations, although the mechanisms are yet to be completely defined (7,12,27,31).
In support of the current findings, Cronin et al. (12) reported that resisted bungy countermovement jump training (performed on a isoinertial supine squat machine) improved a variety of lower-body strength and power measures after a 10-week training phase. Cronin et al. (12) also reported that resisted bungy countermovement jump training produced greater electromyographic activity (70-100%) during the later stages of the eccentric phase of the jump, when compared to the free jump method. Accentuated eccentric loading increases the force that can be produced in the concentric phase of the movement and may be because of increased elastic energy storage as a result of the greater eccentric load increasing tendon elongation (13). Sheppard et al. (33) reported that 5 weeks of accentuated eccentric loading countermovement jump training increased vertical jump height by 11% in high performance volleyball players. The increase was significantly larger than the control group who performed regular countermovement jumps. Therefore, improvements in vertical jump after resisted jump training might also be related to an increased eccentric loading after the flight phase of the jump and similar to those observed after drop jump training.
The free jump group produced a trivial increase in vertical jump. The lack of improvement may be because of the subject's regular use of the free jumps as part of their training program before the beginning of the study. As such, the kinetic components of power that are optimized by free jump training may have been previously developed; thus, there was less potential for adaptation to occur (33).
Inclusion of assisted or resisted jumping (3 sets of 6) twice a week to a conditioning program can improve vertical jump height over a 4 week training phase to levels comparable to that found over a 4-year period in similarly trained rugby league athletes (5). Conditioning coaches and athletes can simply integrate these methods of jump training into their current resistance training via contrast training methods or as a part of their plyometric training sessions. The improvements in jump height in the current investigation were made in well-trained rugby athletes; however, we believe that the improvements are not limited to this form of athlete and should be performed by any athlete where jumping, sprinting, or any explosive lower-body movements are performed in competition. Finally, assisted jumping may also provide a lower impact method of plyometrics, which may be useful for progressing the intensity of plyometric loading after lower-body injury or for heavy athletes who do not tolerate the high impact ground reaction forces on landing. Future research in this area should look at investigating the effects of individualized prescription of assisted compared to resisted jump methods for athletes with limitations in their velocity and force components of power, respectively. When combined with appropriate testing methodologies, such an approach may maximize the potential for power gain in these athletes.
The Waikato Rugby Union and the Tertiary Education Commission provided finical support by way of scholarship for the primary author. The results of the present study do not constitute endorsement by the National Strength and Conditioning Association.
1. Andersen, JL, Klitgaard, H, and Saltin, B. Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training. Acta Physiol Scand
151: 135-142, 1994.
2. Argus, CK, Gill, ND, Keogh, JWL, Hopkins, WG, and Beaven, CM. Changes in strength, power and steroid hormones during a professional rugby union
competition. J Strength Cond Res
23: 1583-1592, 2009.
3. Baker, D. A series of studies on the training of high-intensity muscle power in rugby league football players. J Strength Cond Res
15: 198-209, 2001.
4. Baker, D and Newton, RU. Acute effect on power output of alternating an agonist and antagonist muscle exercise during complex training. J Strength Cond Res
19: 202-205, 2005.
5. Baker, DG and Newton, RU. Adaptations in upper-body maximal strength and power output resulting from long-term resistance training in experienced strength-power athletes. J Strength Cond Res
20: 541-546, 2006.
6. Behm, DG. Neuromuscular implications and applications of resistance training. J Strength Cond Res
9: 264-274, 1995.
7. Blazevich, AJ, Gill, ND, Bronks, R, and Newton, RU. Training-specific muscle architecture adaptation after 5-wk training in athletes. Med Sci Sports Excer
35: 2013-2022, 2003.
8. Blazevich, AJ, Horne, S, Cannavan, D, Coleman, DR, and Aagaard, P. Effect of contraction mode of slow-speed resistance training on the maximum rate of force development in the human quadriceps. Muscle Nerve
38: 1133-1146, 2008.
9. Bottinelli, R, Canepari, M, Pellegrino, MA, and Reggiani, C. Force-velocity properties of human skeletal muscle fibres: Myosin heavy chain isoform and temperature dependence. J Physiol
495: 573-586, 1996.
10. Cavagna, GA, Zamboni, A, Faraggiana, T, and Margaria, R. Jumping on the moon: Power output at different gravity values. Aerospace Med
43: 408-414, 1972.
11. Corn, RJ and Knudson, D. Effect of elastic-cord towing on the kinematics of the acceleration phase of sprinting. J Strength Cond Res
17: 72-75, 2003.
12. Cronin, J, McNair, PJ, and Marshall, RN. The effects of bungy weight training on muscle function and functional performance. J Sport Sci
21: 59, 2003.
13. Doan, BK, Newton, RU, Marsit, JL, Triplett-McBride, NT, Koziris, LP, Fry, AC, and Kraemer, WJ. Effects of increased eccentric loading on bench press 1RM. J Strength Cond Res
16: 9-13, 2002.
14. Drinkwater, EJ, Galna, B, McKenna, MJ, Hunt, PH, and Pyne, DB. Validation of an optical encoder during free weight resistance movements and analysis of bench press sticking point power during fatigue. J Strength Cond Res
21: 510-517, 2007.
15. Dugan, EL, Doyle, TLA, Humphries, B, Hasson, CJ, and Newton, RU. Determining the optimal load for jump squats: A review of methods and calculations. J Strength Cond Res
18: 668-674, 2004.
16. Duthie, GM, Young, WB, and Aitken, DA. The acute effects of heavy loads on jump squat performance: An evaluation of the complex and contrast methods of power development. J Strength Cond Res
16: 530-538, 2002.
17. Hanson, ED, Leigh, S, and Mynark, RG. Acute effects of heavy- and light-load squat exercise on the kinetic measures vertical jumping. J Strength Cond Res
21: 1012-1017, 2007.
18. Harris, GR, Stone, MH, O'Bryant, HS, Proulx, CM, and Johnson, RL. Short-term performance effects on high power, high force, or combined weight-training methods. J Strength Cond Res
14: 14-20, 2000.
19. Hill, A. The heat of shortening and the dynamic constants of muscle. Proc R Soc Lond
126: 136-195, 1938.
20. Hopkins, WG. Probabilities of clinical or practical significance. Sportscience
6. Available at: sportsci.org/jour/0201/wghprob.htm. Accessed June 1, 2008.
21. Hopkins, WG. Spreadsheets for analysis of controlled trials with adjustment for a predictor. Sportscience
10. Available at: sportsci.org/ 2006/wghcontrial.htm. 2006. Accessed June 1, 2008.
22. Kilgallon, M and Beard, A. The assisted jump squat. J Aust Strength Cond
17: 30-32, 2009.
23. Kraemer, WJ and Newton, RU. Training for muscular power. Phys Med Rehab Clin North Am
11: 341, 2000.
24. Kubo, K, Kanehisa, H, Takeshita, D, Kawakami, Y, Fukashiro, S, and Fukunaga, T. In vivo dynamics of human medial gastrocnemius muscle-tendon complex during stretch-shortening cycle exercise. Acta Physiol Scand
170: 127-135, 2000.
25. Larsson, L and Moss, RL. Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles. J Physiol
472: 595-614, 1993.
26. Majdell, R and Alexander, MJL. The effect of overspeed training on kinematic variables in sprinting. J Hum Mov Stud
21: 19-39, 1991.
27. Mangine, GT, Ratamess, NA, Hoffman, JR, Faigenbaum, AD, Kang, J, and Chilakos, A. The effects of combined ballistic and heavy resistance training on maximal lower- and upper-body strength in recreationally trained men. J Strength Cond Res
22: 132-139, 2008.
28. Markovic, G and Jaric, S. Positive and negative loading and mechanical output in maximum vertical jumping. Med Sci Sports Exerc
39: 1757-1764, 2007.
29. Mero, A and Komi, PV. Force-, EMG-, and elasticity-velocity relationships at submaximal, maximal and supramaximal running speeds in sprinters. Eur J Appl Physiol Occup Physiol
55: 553-561, 1986.
30. Newton, RU and Kraemer, WJ. Developing explosive muscular power: Implications for a mixed methods training strategy. Strength Cond J
16: 20-31, 1994.
31. Newton, RU, Kraemer, WJ, and Häkkinen, K. Effects of ballistic training on preseason preparation of elite volleyball players. Med Sci Sport Exercise
31: 323-330, 1999.
32. Newton, RU, Kraemer, WJ, Häkkinen, K, Humphries, BJ, and Murphy, AJ. Kinematics, kinetics, and muscle activation during explosive upper body movements. J Appl Biomech
12: 31-43, 1996.
33. Sheppard, J, Hobson, S, Barker, M, Taylor, K, Chapman, D, McGuigan, M, and Newton, R. The effect of training with accentuated eccentric load counter-movement jumps on strength and power characteristics of high-performance volleyball players. Int J Sport Sci Coach
3: 355-363, 2008.
34. Vescovi, JD and McGuigan, MR. Relationships between sprinting, agility, and jump ability in female athletes. J Sport Sci
26: 97-107, 2008.
35. Young, WB, Jenner, A, and Griffiths, K. Acute enhancement of power performance from heavy load squats. J Strength Cond Res
12: 82-84, 1998.
Keywords:© 2011 National Strength and Conditioning Association
elite athletes; in season; vertical jump; rugby union