This articles addresses the drop jump test outcomes with regards their value for individualized athletic training.
Relevance for the Sport
The outcomes of the drop jump test bear value for coaches to implement individualized training programs for the following purposes:
- Enhance general reactive strength performance
- Identify potentials for increasing injury resistance
Many individual and team sports require athletes to generate explosive muscle power in the lower limbs. Examples are soccer, football, basketball, athletics or tennis. Athletes in these sports must be capable to rapidly increase velocity and produce maximum force. Often, the athletic movements are critical with regards to timing, meaning force must be produced at a very specific time in the movement. Often, there are also time restrictions for the development of force (1).
This article is dedicated to highlighting how important outcome metrics can be determined by means of the ReGo Drop Jump Test. In general, the Drop Jump Test is one option to test the reactive strength, coordination and timing capabilities of an athlete. In particular, vertical jump height is a reliable predictor of success in many sports as it depends on the development of speed-strength and power (2–4).
The drop jump test is a standard test in performance diagnostics to measure explosive leg power (5) and the ability to deploy fast stretch-shortening cycles of the affected muscles as described in the stretch-shortening cycle (SSC) function (3, 6, 7, 8). The RSI can also be used as a readiness-to-train marker (9). Furthermore, the findings of a research study (10) imply that determining loading patterns during rebound may allow preventive measures to avoid stress pain and potential injuries.
The drop jump test is a double-legged jump test and involves dropping from an elevated platform onto the ground with both feet, absorbing the drop and immediately propelling back up (rebound) into a maximal vertical jump and a final landing, as shown in Fig-1. The test poses a fast stretch-shortening movement on the lower extremities as the eccentric landing phase is amplified by means of the dynamic drop component.
Hands should rest on the hip throughout the test for consistency with regards to intra-individual and inter-individual comparisons. Keeping hands on the hips will, however, reduce the ability to create rebound energy as the arms cannot be used to create dynamic swing power. This is also why outcomes with and without arm swing cannot be compared against each other.
Fig-2 shows the compound ground reaction force (GRF) curve of the left and the right leg for one complete Drop Jump execution. The different test phases are highlighted along with particular points of the stretch-shortening cycle (SSC) which relate to specific muscle activity patterns.
Last but not least, it must be considered that the drop jump test requires a solid musculoskeletal development as it poses a great amount of stress to the locomotion system. Drop Jump tests should not be performed after injuries unless the athlete is fully recovered.
Follow the link for a more detailed test description of the ReGo Drop Jump Test, including a step-by-step guide and an instruction video.
Outcome Parameters for Reactive Strength
The drop jump test is primarily applied to quantify the quickness and reactivity of an athlete in the transition from absorption to propulsion throughout the first land and rebound movement. A key outcome parameter is the reactive strength index (RSI). The RSI is defined as the ratio between jump height and ground contact time (11).
A large RSI value indicates that the athlete is able to produce a great jump height and at the same time minimizing time on the ground during rebound (12). The larger the RSI value, the better the athlete’s performance. In competition, it is often a decision between goal and loss if actions which include propelling into the air can be performed extremely quick. Examples are jumps to the ball in soccer or offensive and defensive rebounds in basketball.
If RSI is low, have a look at ReGo Ground Contact Time and ReGo Jump Height to identify which aspect bears most potential. Train speed if ground contact time is large. Train strength and agility if jump height is low.
The ReGo Drop Jump Test Report provides both the basic RSI metric as well as important single metrics such as the Rebound Jump Height or the Ground Contact Time (Fig-3 left). This is because for trainers, it is important to know if their athletes should rather train speed (Ground Contact Time too long) or strength and agility (Rebound Jump Height too low). The Ground Contact Time is further divided into the Braking Phase and the Propulsive Phase for analyzing concentric and excentric muscle performance (Fig-3 right). These single metrics allow further insight into how the stretch-shortening cycle (SSC) can be improved by means of training concentric or excentric abilities, respectively (12).
The Peak Force and the Jump Impulse indicate the magnitude of force in the athlete’s foot-to-ground interaction and the vertical force over time put into the ground while the foot rests on the ground, respectively (Fig-4). The Jump Impulse is represented by the area under the force curve encompassing the complete rebound phase from initial ground contact to takeoff.
From a trainer’s perspective, it is important to know these metrics to create individualized training interventions as Peak Force and Jump Impulse may correlate in different ways. For instance, an athlete’s ability to generate a great amount of force in little time (Fig-5 left) may result in the same amount of Jump Impulse as another athlete who enerates little force over a longer time (Fig-5 right). The latter for sure does not contribute to high RSI values. In effect, Ground Contact Time should be analyzed along with Peak Force and Jump Impulse to see if an athlete’s abilities develop in the right way.
Outcome Parameters for Load Distribution & Coordination
In addition to the reactive strength parameters, the evaluation of load patterns and aspects of foot coordination present important measures of musculoskeletal control, particularly with regards to the ability to stabilize the ankle joint during rebound and, to some extent, to evaluate varus-valgus displacements.
The findings of a cross-sectional study (10) indicate that subjects suffering from patellofemoral pain show higher medial-to-lateral peak forces in the drop jump compared to individuals without knee pain. In this respect, the evaluation of loading patterns can be useful to identify potentials to reduce risks of injury.
Fig-6 shows two sets of examples for the ReGo Drop Jump Test Report parameters related to load Load Distribution, Rebound Point and Sway Area which contain the outcomes of drop jump executions of two different athletes. The Load Distribution (Fig-6 left) displays the distribution of loads during the rebound phase, shown as percentage of the total load in six segments. It indicates if an athlete is able to perform the rebound on the forefoot, keeping the ankle joint tight, without hitting the ground with the heel as described in the general drop jump task. Further, the widget shows if a medialization of loads was evident which may lead to joint overstress in the ankle joint and in the knee joint.
Train ankle stiffness if ReGo Load Distribution shows significant heel loading and ReGo Rebound Point moves towards mid-foot. You may use pogo jumps or skips. Train dynamic stability if the ReGoSway Area is too large. You may use single leg balance boards or sticket hops.
The Rebound Point and the Sway Area indicate the mean center of pressure (COP) during rebound and the variation of the COP as measures for the position of the foot on the ground and foot stability, respectively. The sway area is formed by an ellipse which includes 95 % of all COP points measured during rebound. Its semi-axes represent the medial-lateral and the anterior-posterior COP variation. Its degree of rotation indicates the preference orientation of the cloud of COP points as an indicator of the direction of foot movements during rebound (19).
Tips for Athletic Training
To generate explosive muscle power, athletes need to produce high levels of force and speed at the same time. Therefore, resistance training combined with plyometric training is an effective way to increase speed-strength and power.
1. Resistance training
An important factor to improve power is strength training. Maximum strength is related to power output and is arguably advantageous in many sports (1).
2. Plyometric training
Plyometric training exercises utilize the SSC and improve jumping, sprinting, and agility performance (12). For instance, a meta-analysis demonstrated that 12 weeks of plyometric training increased drop jump performance in women (13).
Due to the force requirements of plyometric exercises, make sure the athlete has a good general level of strength before starting plyometric training (8, 14). Further, plyometric training exercises should only be performed after an adequate warm-up and in a fully recovered state. All subsequent exercise recommendations are adapted from literature (14, 15).
The following exercise tips refer to plyometric training for enhancing reactive strength starting from a medium fitness level.
| o Start in an upright stance with slightly bent knees
o Keeping the knees slightly bent and using only the lower legs, begin a vertical takeoff
o Emphasize more flexion and extension in the ankle, than in the knee joint
o After takeoff, keep the foot in a toes-up position
| o 4 sets with 4-6 repetitions per session
o Rest between repetitions: 5 – 30 seconds
o Rest between sets: 30 – 90 seconds
The following exercise tips refer to plyometric training for enhancing reactive strength for advanced athletes.
| o Begin in an upright position, feet shoulder-width apart
o Interlace fingers and place palms at the back of the head
o Bend the knees to get into a half-squat position
o Immediately reverse the downward movement and jump up as high as possible
o Extend the hips, knees, and ankles, land in the same position as takeoff
o First, stick the landing, reset and start the next repetition
o Progress to performing multiple repetitions without a break in between
| o 4 sets with 4-6 repetitions per session
o Rest between repetitions: 5 – 30 seconds
o Rest between sets: 30 – 90 seconds
The following exercise tips refer to plyometric training for enhancing reactive strength for top level athletes.
|Box Jump (multiple response)
| o Equipment: Box, bench, or any elevated, stable platform (height: 30 – 60 cm)
o To start, face the box and slightly bend the knees
o Use the arms to help lift while jumping upward and forward to land on the box
o Drop or jump back down immediately to start again
o Note: if knee flexion during landing is greater then during takeoff, reduce the height of the platform
| o 5 x 6 repetitions per session
o Rest between repetitions: none
o Rest between sets: 30 seconds to several minutes
Comments on Measurement Equipment
Traditionally, Drop Jump outcome metrics are determined either using force plates, contact mats or light switches (16). All options typically deliver good to excellent accuracy for the RSI, but are permanently installed in one place or harder to move. Force plates allow detailed analysis of the ground reaction forces, often for left and right foot separately (17).
ReGo Sensor Insole introduce a new, valid and reliable (18) opportunity for testing athletes in any place, outside performance labs or training facilities. If intertial sensors for temporal-spatial parameters are combined with plantar pressure distribution readings (as in the ReGo Sensor Insoles), additional outcomes such as load distribution, force symmetry and variability of the foot’s center of pressure can offer valuable insights into an athlete’s ability to control the locomotor system during plyometric exercises, as shown in this article.
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17. Hawkin Dynamics Staff. Understanding the Drop Jump Test – The Basics. Hawkin Dynamics Blog. February 25th 2019, https://www.hawkindynamics.com/blog/understanding-the-drop-jump-test-the-basics.
18. Cramer LA, Wimmer MA, Malloy P, O’Keefe JA, Knowlton CB, Ferrigno C. Validity and Reliability of the Insole3 Instrumented Shoe Insole for Ground Reaction Force Measurement during Walking and Running. Sensors: March 2022 – Volume 22 – Issue 6 – https://doi.org/10.3390/s22062203.
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