Check out Part 1 here: Plyometric jumps: Shock tactics part 1
Many coaches want to know how many drop jump sets and ground contacts should be incorporated into a session…
Adding resistance to drop jumps
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Drop jumps can be performed more obviously with the athlete wearing a weighted vest or carrying dumbbells or with a barbell/Powerbag across their shoulders. Less obvious is the use of resistance bands that are designed to increase the reactivity of the transition into the concentric part of the jump. Malaysian researchers, although using the counter movement jump (CMJ) for analysis, produced some very interesting results, which could be translated to the drop jump. The CMJ requires the athlete to lower (absorb more when compared to a drop jump) and extend their legs in order to jump for height.
Fifteen trained males performed three types of CMJ: one used no added downward tensile force and the other two downward tensile forces equivalent to 20% and 30% of the performers’ body mass. So, how did the researchers add this downward tensile force? The athletes flexed their thighs in preparation for the jump (the ‘counter movement’ part), whilst attached to an elasticised-type harness which increased resistance as indicated, on leaping upwards the harness was released. (Thus they were pulled down into the jump using the elastic properties of bands). The researchers discovered with CMJ against 30% resistance, the maximal concentric vertical ground reaction force was increased by 6.34%, power output by 23.21% and jump height by 9.52%.
The very positive results of this innovative study have some very interesting applications for the drop jump. It’s possible that jumps from a height that is seen to develop strength (1.50m according to Verkhoshansky) could have their reactivity enhanced by the use of downward tensile force – thus closing the gap between developing strength and maximum strength in one drop jump. Likewise jumps from a lower platform-height (optimised between 50-75cm) could have their reactivity speed super-enhanced by the use of this training methodology.
So what about the reverse scenario – adding resistance?
Verkhoshansky carried out a number of experiments and concluded that adding resistance did not improve jump performance. Specifically adding resistance decreased the height of the jump on landing and slowed reactivity, compared to un-loaded jumps – more on this when we consider jumping angle.
Another variable that can affect the specific outcome of drop jumping is the angle of the subsequent jump/jumps after landing i.e. whether it’s for height, or distance or a combination of the two. Spanish researchers looked at previous drop jump research that considered jump angle as well as extra resistance and the effects this had on sprinters. Twenty-six studies were included in the research and after analysis and it was discovered specifically in terms of improving sprint performance and drop jumps that, “….. To optimise sprint enhancement, the combination of different types of plyometrics and the use of training programmes that incorporate greater horizontal acceleration (i.e. sprint specific plyometrics), jumps with a horizontal displacement would be recommended.”
Additionally and corroborating the works of Verkhoshansky, no benefit was to be found from adding resistance to plyometric exercises. Thus the take-home value for sports coach and athlete alike is to carefully analyse their sport and develop a programme of drop jumps (and other plyometric exercises) that have as close a resemblance as possible to the key jump and movement patterns involved in their sport. Suitable drop jumps for developing sprint speed, for example, could involve jumping from a 50-75cm platform to land on one leg and perform two hop or three bounds and so. Another innovative drill would be to land on two feet and then immediately sprint 15m. The athlete must absorb the landing (quickly remember) and then move one foot forward extremely rapidly to sprint away. This drill requires a lot of mental effort and taxes the central nervous system (CNS) in particular – of which more later.
Many coaches want to know how many drop jump sets and ground contacts should be incorporated into a session. There is no simple answer to this one, as the training maturity of the athlete, their experience and the time in the training year will all impact on this decision. However, perhaps the key consideration – once the athlete is able to perform the plyometric exercise (whatever it is) with optimum technique – is quality. As has been stressed if reaction time begins to slow as indicated by a decreasing vertical or horizontal distance achieved or perhaps more pertinently by an increase in ground contact time, then the session is best truncated.
Training at sub-optimal speeds will elicit overtime sub-optimal transference into the athlete’s sport. It’s probably the case that a ‘less is more’ approach should be adopted when it comes to drop jumps. The CNS acts as a control centre for the body with much debate raging over how much of it functions at the conscious or subconscious level. In terms of sports training it relays and interprets signals, stresses and responses from around the body and this includes the shock forces associated with drop jumps and other plyometric exercises. If CNS fatigue is allowed to build up – in one session or over a training period and in particular a competitive period, then the ‘drain’ on the CNS can be deleterious to sports performance.
How is this so?
The athlete may be unable to react as quickly as he would when performing a drop jump, for example and this could lead to a declining beneficial yield in terms of adaption form the activity into performance (in extreme cases it could also lead to over-training and injury). Spanish researchers discovered as indicated that a less is more approach may be the most successful drop jump training approach. Their research involved 3 different drop jump volumes – 1 day, 2 days and 4 days a week. Maximal strength, vertical jump and sprint performance were evaluated as outcomes of these programmes. The 1- day-a-week group performed 420 jumps in total, the 2-days-a-week group, 840 jumps and the 4-days-a-week group, 1680 jumps.
There was also a control group and the survey lasted 7 weeks. Three different drop heights were used for the drop jumps – 20, 40 and 60cm (heights that would elicit a greater speed component than strength one). Maximal strength (1 repetition maximum [1RM] and maximal isometric strength), vertical height in counter-movement jumps and drop jumps and 20m sprint time tests were carried out before and after the 7 weeks of plyometric training. It was discovered that the 2-day-a-week protocol produced similar enhancements in jumping performance, but with greater training efficiency (approximately 12% and 0.014% per jump) compared the 4-days-a-week, training frequency (approximately 18% and 0.011% per jump).
In addition, similar enhancements in 20m-sprint time, jumping contact times and maximal strength were observed in both 2-day and 1-day-a-week groups compared with the high training frequency group. Thus, in a time-crunched training programme the benefits to be gained by performing more drop jump sessions, rather than fewer seem limited. The drop jump offers both athletes and coaches a great training tool. However, for athletic performance to be optimised through its use a number of crucial variables must be carefully considered. Understanding optimum drop-height is particularly crucial as is the avoidance of adding additional loading. Equally important ground contact times must be optimised and take-off angles utilised that replicate as closely as possible the sport that the athlete is training for. Drain on the CNS must be monitored and in the light of this, a more circumspect approach over their use rather than a judicious one would seem prudent.