Drop Jump or Depth Jump?
Based off of our research and for the purpose of this article, a drop jump will be classified as anything with a ground contact time (GCT) of < 250 ms.
This < 250 ms GCT is deemed a quality of the "fast stretch-shortening cycle" or fast SSC. Whereas, slow SSC is classified as anything > 250 ms GCT.
Anything that falls into this slow SSC category is considered a depth jump.
This is not absolute, as some sources may classify these two jumps differently. However, this is how we interpret the difference between the two.
Therefore, the distinction between a drop jump and depth jump is the difference in GCT. A depth jump is typically completed from a taller drop box height when compared to a drop jump. This is typically why a longer/slower GCT is needed to produce the reciprocal concentric muscle action during a depth jump. Greater knee flexion and a greater torso angle is also indicative of a depth jump.
Profiling Drop Jumps & Depth Jumps
First thing you need to do is determine a good starting drop box height for your drop or depth jump. If you are unsure of a good starting drop box height 15 cm is a good place to begin. This will ensure that the athlete is warmed-up and that they also don't start at a drop box height that is too high.
Next, you will want to have a device to record GCT, Jump Height (JH), and Reactive Strength Index (RSI) such as the Exsurgo gFlight. Simply place the gFlight on the ground about stepping distance from the drop box. You want to have the athletes step off and have their pinky toes land on the "invisible" line that the gFlight creates between two units. If you are working with a novice athlete it may be a good idea to place a piece of tape along the ground to create a visual marker for proper landing.
Once you have your gFlight in place have the athlete step off of the drop box (without stepping down) and allow gravity to bring the athlete to the ground. Cue the athlete to create stiffness upon impact.
Immediately upon impact have the athlete jump vertically as quick and high as they possibly can. Record the JH, GCT, and RSI for the jump.
Last, you should decided what quality you are looking to train with that specific athlete (fast or slow SCC, i.e. drop or depth jump). Considerations should predominately be based on demands of the sport and also experience of the athlete.
Once you have determined if you are after a fast SCC or slow SCC, you can begin adding or subtracting drop box height to reach the desired quality.
Increase or decrease drop box height until your athlete obtains a GCT of < 250 ms. Once this is achieved record the RSI value at the drop box height. Slowly add height to the drop box height until GCT exceeds 250 ms. Your goal should be to obtain the highest RSI value with a GCT of under 250 ms (generally speaking, some sport demands may have a quicker GCT demand). JH should also increase, as this is an outcome you are also looking to improve.
In order for RSI to increase the athlete wants to decrease GCT, while also increasing JH.
RSI = JH / GCT
Drop jump variations are essentially endless. Examples include traditional drop jumps from a low/medium drop box height, pogo jumps, jump rope, continuous low/medium height hurdle jumps, and bounding.
Increase drop box height until you obtain a GCT value at or above 250 ms. One should consider that there is a point of diminishing return on GCT values. If the GCT value becomes too large, the athlete will lose most of the energy transfer from eccentric to concentric muscle action. However, since a depth jump is classified as longer GCT or "slow SCC" above 250 ms is a good starting value. The goal here should still be to obtain a high RSI value, however you will want to have an emphasis on increased JH here. If JH starts to diminish, the drop box height is probably to high.
Depth jump variations are more narrow in terms of possible exercises. The two main examples of a depth jump are dropping from a tall drop box height and also a continuous hurdle jump using a tall hurdle. The continuous tall hurdle demands a longer GCT upon landing because of the larger displacement of movement over the hurdle.
Depth jumps are typically much more intensive than drop jumps and should be programmed with caution. Considerations should include training age, training phase, and other external stressors.
Once you have determined the point of diminishing return for the quality you are after (fast or slow SCC), the athlete should then train at this drop box height.
Slowly increase volume first at the drop box height before increasing drop box height itself. Once you have done this and the athlete can maintain a good RSI value, the athlete is then ready to increase drop box height.