December 13, 2017

A spreadsheet for Sprint acceleration Force-Velocity-Power profiling

Written with Dr Pierre Samozino (University Savoie Mont Blanc)

Due to popular demand and frequent requests from sport practitioners and researchers, we have decided to publish a spreadsheet and tutorial for implementing our sprinting FVP field method based on split times measurements during a 30-m, all-out sprint acceleration, from a standing (2 or 3-point) start. This simple method has been initially proposed and validated against force plate data by Samozino et al. in 2016, and used afterwards in several publications (see here).

Download this spreadsheet HERE.

Watch the 10’ video tutorial here: 

This spreadsheet will automatically calculate the sprint force-velocity profile based on the following input variables: 5 split times over a 30 or 40-m acceleration, air temperature and pressure, stature and body mass of the athlete, based on the modeling of the position-time curve by an exponential function. 
After a quick adjustment of the 2 variables of the exponential model (maximal velocity Vmax and time constant Tau) to fit the actually measured split times, it will automatically display the FVP curves, the main mechanical outputs and the mechanical effectiveness. Note that you will need to install/use the Excel Solver add-in macro for this adjustment. 
For full details on the definition and practical meaning of these variables, please read this commentary paper.
In addition to exploring your athlete’s performance, it will indicate the underlying mechanical variables, and help you design more effective, individualized training content.
Furthermore, in the context of rehabilitation and return-to-sport processes, knowing an athlete’s pre-injury profile is gold to an effective, sprint-oriented rehabilitation and return-to-sport decision. See Jurdan Mendiguchia’s works on the topic in 2014, 2016 and 2017.
This “profiling” test may be done with only 4 split times (5, 10, 20, and 30m), but for more accuracy we recommend using 5 or 6.

As to the devices needed, well, it’s up to you, any device that accurately measures split times may be used: timing gates, iOS app MySprint, etc… But one thing is important to keep in mind: the most important thing to ensure that the measurements are valid and the data make sense is that the time measurement starts as soon as any propulsive action is produced. So what we recommend if you are using timing gates and not the iOS app MySprint, is that a system that reacts to the athlete’s first propulsive action triggers the timing (see review here). In case of a trigger by a first pair of cells (eg 20 or 50 cm in front of the athlete’s starting position), the split times will be underestimated, and thus F0 and Pmax variables will be largely overestimated. This is how soccer players are sometimes described as “faster than Bolt” in the News! When using this starting procedure, the athlete’s body has in fact a high forward velocity at the moment of triggering, which leads to erroneous values and performance/mechanics overestimations. For the same reasons, a standing start from a still position must be used.

Finally, this is a short list of normative values for the different mechanical variables, ranging from physically active (male) individuals with no specific sprint experience to elite athletes (mostly rugby players or sprinters), based on our own experience (please see the literature on the topic for more details).

F0 (N/kg): from 3-4 to 10-12 N/kg
V0 (m/s): from 5 to 12 m/s
Pmax (W/kg): from 6-7 to 25-30 W/kg
RF max (%): from 20 to 60%
Drf (%): from -10 to -4%

Note that our group will soon publish an extensive database for both male and female athletes. 
Should you obtain values beyond these standards, don’t blame the method or the spreadsheet, the issue is with the device used to measure split times, and/or the starting/triggering procedure. See our recent discussion on these overestimations here.

Using this model, this is the FVP profile of Usain Bolt during the current 100-m World Record:
Usain Bolt's 100-m record force-velocity-power profile

Ready, Set, Enjoy! 

October 1, 2017

A spreadsheet for jump Force-Velocity-Power profiling

Written with Dr Pierre Samozino (University Savoie Mont Blanc)

Due to popular demand and frequent requests from sport practitioners and researchers, we have decided to publish a spreadsheet and tutorial for implementing our jumping FVP field method based on jump height measurements during loaded squat jumps. This simple method has been initially proposed and validated against force plate by Samozino et al. in 2008, and afterwards adapted to countermovement jump by Jimenez-Reyes et al., and recently to bench press by Rahmani et al.

Download this spreadsheet here: (Linked Data)

Watch the 10’ video tutorial here:

Basically, this spreadsheet will automatically calculate the jumping force-velocity profile from jump height, loads used and the anthropometrical data of the athlete (body mass, lower limb length) based on the equations validated in 2008 by Samozino et al. It will also display the optimal profile (i.e. the profile that would maximize jump height for this athlete) and the “force-velocity imbalance”, which will help design more effective, individualized training content. Links to all the papers are inserted in the spreadsheet in case you want to know more about the concepts, models, validations. This is definitely a science-based approach of jump training, and this applies to vertical but also inclined push-offs like sprint start in running or swimming (see my previous blog post on the latter topic).

This “profiling” test may be done with only 2 loaded jumps, but for more accuracy we recommend using 4 or 5 loads. The spreadsheet allows you to check this accuracy and decide your best practice.

As to the devices needed, well, it’s up to you, any device that accurately measures jump height may be used: force plate, Optojump, jumping mat, linear position transducers, iOS app MyJump2, etc… But one thing is important to keep in mind: there are systematic differences in jump height measurements between some of these devices (e.g. between force plate / MyJump and Optojump) for some technical reasons. Consequently, you should be consistent and always use the same device to monitor / compare athletes’ data over time, and you should not profile athletes based on jump height measured with one type of device and compare to data measured with another type of device.

In addition, note that the spreadsheet may also be used to compute countermovement jump FV profile, provided that the downward movement depth is controlled and accurately taken into account in the calculation of the starting height.

The following tips for a correct testing procedure (and thus a highly linear FV relationship and R2 close to 1) are based on our extensive use of the approach and hundreds of profile tests performed:
  • Make sure the athlete is familiar with loaded jumps up to additional mass close to his/her body mass. Several preparation sessions may be necessary, but it is worth it to ensure accurate and reproducible measurement. 

  • A 5 to 10-minute general warm-up should be performed (e.g. running, cycling or rowing) followed by a specific warm-up with vertical jumps and a progressive increase in the intensity and loaded jumps, which contributes to avoid any apprehension of this kind of exercise and benefit from a possible potentiation effect. 

  • We recommend 2 trials per load condition, and should jump height differ between the trials by more than 5%, a 3rd trial should be performed. The spreadsheet displays the profile “linearity” as you enter the loads-jump height so you can easily check what trial was “wrong” i.e. not aligned with the others

  • If the starting position is freely chosen (knee angle about 90°) by the athlete, they will get to this position very consistently so you may not have to thoroughly check for this starting height. One way to verify this is to ask the athlete during the warm-up to get to this positon with different loads on the shoulders. You will normally measure the same starting height if this is the preferred starting height of the athlete. It’s important to measure it after warm up since it is always quite different after compared to before warm-up. Our observation is that this starting height is very consistently reached if the athlete has chosen it as the most comfortable position, and if they are focused during the trials. So maybe not necessary to lose time systematically checking for this. But remember starting height influences push-off distance, which influences jump height…

  • The range of loads chosen should be as large as possible: from 0 kg (squat jump) to the load that leads to a jump height of about 10 cm. Typically, for a trained soccer player of 80 kg, we use 0, 20, 40 and 60 kg in a randomized order. For athletes used to strength training, the maximal additional load can be their body mass or even heavier. 

  • In case of very strong/heavy athletes, the maximal load may be lower than body mass, if the range of load is large. 

  • Note that the jumping FV profile is linear in nature, so we use absolute loads, which greatly simplifies testing procedures. It is not necessary to calculate and set relative loads (as % of body mass or % or squat 1RM) since the F and V values obtained will align on the same line as those obtained with absolute loads…so you can save time here. 

  • Always remember the main sources of bias in the jumping technique: there should be no trunk movement priori to push-off; no downward countermovement; take-off with lower limb full extension and land in the same position (i.e. no knee flexion, feet in full plantar flexion) when jump height is obtained from aerial time; jump with all-out effort intention.