LEADING DROP JUMP METHOD AND METRICS BY HAWKIN DYNAMICS

To kick off 2025, Hawkin Dynamics has updated its drop jump analysis method to take accuracy to the highest level. The gold standard and now Hawkin Dynamics’ preferred approach to drop jump analysis comes in the form of the reverse integration method, which only requires the athlete to remain still for at least the final second of data capture to work (Baca, 1999; McMahon et al., 2022; Wade et al., 2022). This method allows for precise calculation of jump height and all other performance metrics by accurately estimating the athlete’s true drop height, which is almost always different from the height of the box or platform they start on. Knowledge of true drop height allows the precise calculation of the athlete’s velocity (specifically, the velocity of their body’s center of mass) when they contact the force plates, which is then used to accurately calculate the velocity-time curve for the entire jump. This is important for accurate phase identification, as well as the calculation of velocity metrics, power metrics, and jump height (calculated from takeoff velocity, as recommended), to name a few reasons. This methodological approach was also advocated as the best option in a systematic review published just two months ago (Eythorsdottir et al., 2024).

If the athlete does not remain still during the last second of data capture but they at least land back on the force plates after the jump element of the test, the Hawkin Dynamics system defaults to the first fallback method, which is the flight time method. This method estimates jump height based on the duration of the athlete's flight (airborne) phase and then uses this jump height value to estimate the preceding drop height and adjusts the velocity-time curve and associated metrics as mentioned further above (Baca, 1999). A potential source of error associated with this method arises if athletes extend their flight phase by tucking their legs (flexing hips and knees) so it’s important to coach athletes to avoid doing this, as it is for all jump tests. However, we have included this method to allow customers to still be able to collect more accurate drop jump data (compared with the final method explained below), even if a final weighing period was impossible. It also produces relatively similar results to the gold standard reverse integration method (see the figure below). An important point to note is that Baca (1999) suggested that due to the possibility for athletes to tuck their legs subtly by differing amounts, this method is better suited to comparing individual athletes’ drop jump performances over time rather than collating group-level data, as might be done when compiling population-specific normative or baseline data.   

These are Bland-Altman plots for drop fall height (left) and jump height (right) calculated by the gold standard method and the flight time method. 

In cases where the athlete does not land back on the force plates at all (which hopefully seldom happens but is possible), the box height method is employed. This method uses the known height of the box or platform relative to the top surface of the force plates (as inputted by the user) and the understanding of free-falling physics to estimate all associated drop jump metrics. This is the Hawkin Dynamics second fallback and legacy method, which has been used in 99% of scientific studies that involved the drop jump test and other force plate software, but it assumes that box height and free fall height (i.e., drop height) are the same. This is an assumption that is often violated due to athletes jumping off or stepping down from the box, even if only slightly (Costley et al., 2018). The extent of the discrepancy between box height and drop height is illustrated by the data shown in the figure below. The box height used was 0.30 m higher than the top surface of the force plate (a very common box height), but the range of true drop heights was between 0.13 m and 0.40 m, which is a staggering 57% below to 33% above the box height. All athletes whose data was included in the figure below were cued to leave the box in the same way, and the tester did not visually spot any meaningful lowering or raising of their center of mass before they dropped from the box. Thus, it is not an easy error to avoid. It is important to note that the box height method would be accurate if athletes could actually drop from the exact height of the box and do so repeatably.    

Each circle in this figure represents an individual athlete’s true drop height, as calculated using the gold standard reverse integration method. 

Knowledge of the true drop height is also fundamental to permit an informed interpretation of drop jump metrics, either when tracking individual athletes’ changes over time or comparing athlete-to-athlete. For example, if two athletes weigh the same (let’s assume 75 kg) and both achieve the same reactive strength index value (let’s say 1.8) during the drop jump test performed from a 0.30m box, the coach might infer that both athletes performed equally well in that test. But what if one athlete’s true drop height was 0.28 m (which is not too bad), whereas the other athlete’s true drop height was 0.20 m (clear lowering)? Well, that difference would result in the contact velocity (when they impact the force plates) being 0.36 m/s less for the athlete who lowered more before dropping and would, therefore, result in a reduced braking net impulse requirement (by 27 Ns) or, in other words, a 15% decreased braking demand. In addition to the drop jump method change, we now also report the drop height metric to allow users to be better equipped to interpret drop jump results and how they change over time. This fundamental metric is missing from most published drop jump research due to those studies not using the reverse integration method, thus leaving a huge question mark over most findings. 

To summarize, Hawkin Dynamics prioritizes the reverse integration method for its precision, defaults to the flight-time method when necessary, and uses the box height method as a last resort. The exact method applied will be known to the user via an automatic tag added to the trial in the cloud. This methodological change to our drop jump analysis protocol is designed to provide customers with the best option whenever possible, which is the #HawkinDifference. It only requires customers to cue their athletes to remain as still as possible at the end of the drop jump data capture, which is very straightforward, just like they do at the start of all other jump test protocols. After all, it is much easier to coach an athlete to stand still after jumping than it is to coach them to precisely drop off a box but, of course, we still should always strive to coach athletes to drop from as close to the height of the box as possible. An example of how to conduct the drop jump test to achieve the final one second of standing still is shown in the video below. Please note that standing back upright after landing will result in a quieter standing still phase versus remaining in the crouch/squat position, thus we recommend this approach for better data accuracy (as shown in the video). We are super excited about this change, and we hope you are too. As always, you can reach out to us if you have any questions whatsoever about the drop jump method change or the drop height metric by emailing techsupport@hawkindynamics.com for a prompt response. Also, we will be following up with several blog posts and resources about the drop jump method change and what it means for our users in the coming weeks, so please keep an eye out for those.