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This protocol describes the execution of a standardized exhaustive jump protocol, a cryotherapy recovery modality, and a non-invasive assessment of recovery characteristics. The protocol of this randomized controlled trial provides several advantages compared to traditionally performed methods in the field of post-exercise recovery studies. Previous studies showed that jump protocols consisting of 100 jumps are a valid method to induce local muscle damage36,37. Ferreira-Junior et al. used a jump protocol consisting of five sets of 20 drop-jumps from a 0.6 m box, with 2 min rest intervals between the sets, to induce muscle damage of the frontal thighs36. Whereas other traditional exhaustion protocols require expensive or mechanical devices38, the current protocol induced muscular exhaustion without the use of any mechanical device. Researchers do not need to buy or rent expensive devices to induce muscular exhaustion or damage to the frontal thighs.
The recovery interventions were applied using a continuous programmable cooling and heating device that can deliver cold or heat to a specific area of the body. Two thigh cuffs were applied around both thighs in supine position for 20 min. Although CWI is one of the most promising methods of enhancing recovery39, the transportation and the necessary amount of water are two challenging factors for the execution of this intervention. Furthermore, to guarantee the ideal water temperature, an additional person is needed to monitor and add ice.
An advantage of the present protocol is the use of an automated and portable cooling and heating device that ensures a constant temperature during the cuff application. Another advantage of the described protocol is the possibility of assessing subjective and objective recovery characteristics without taking blood samples from the participants. The subjective ratings, DOMS (VAS; 0-10 cm) and RPE (BORG; 6-20), used after an exhaustive protocol have been described in numerous published articles24,40,41,42. The assessment of CMJs, as presented in the present protocol, shows a high test-retest reliability (intra-class correlation coefficient (ICC) between 0.48 and 0.88) and validity25,26.
There are some critical steps within the protocol that may present potential sources of error. Two researchers must observe, verbally encourage, and correct the participants during the exhaustive CMJs (3 x 30). The objective monitoring of maximum CMJs may be ensured using accelerometers or linear transducers. Another critical step is the application of the two thigh cuffs. To avoid any compression effects43,44, the cuffs must be wrapped around each thigh with a minimum level of pressure. The application of the cuffs with a minimum of pressure might take a couple of practice runs to master.
The present protocol has some limitations. The 30 s rest period between the sets of the exhaustive jump protocol is very short, and the cardiovascular impact is very high. Another limitation is the ready-to-use lubrication mixture for the recovery modality. It is important to take into account that the heat capacity of this lubrication mixture (i.e., propylene glycol and demineralized water) is slightly lower than that of normal water. The familiarization session of 5 jumps might be too small when the study population is not as physically active as described in the present protocol.
Finally, the assessment of CMJs presents the opportunity to assess objective recovery characteristics. Bishop et al. demonstrated a cheap and practicable method to assess jump height with the mobile-based app "My Jump," which has been shown to be a reliable method for measuring this variable45,46. However, Rowsell et al. indicated that no apparent reductions in CMJ height during a 5-day follow-up period could be observed after exhaustive soccer tournament matches24. Rupp et al. observed similar results after an exhaustive endurance test34. These results are in line with the results of the presents study, showing that the assessment of CMJ height might not be sensitive enough to measure the amount of muscular exhaustion.
In this protocol, the cold application temperature was set at 8 °C, whereas the temperature of the thermoneutral application was set at 32 °C. It has been demonstrated that cold water temperatures are normally ≤20 °C and that thermoneutral water temperatures have a range from 24 °C to <36 °C47. It is important to consider that the amount of adipose tissue significantly affects the tissue cooling rate, with thicker skinfolds requiring longer application times48. Researchers should modify the cooling temperature and application duration according to their research populations.
Future studies should consider that the assessment of the maximum voluntary contractions of the knee extensors might be a more sensitive assessment of objective recovery characteristics compared to CMJs49. For this protocol to be effective, it is crucial that the participants perform a familiarization session for the CMJs. Future studies using a different study population than that described here should increase the number of jumps to guarantee a familiarization effect. Additionally, future studies might increase the resting time between the exhaustive CMJs to guarantee maximum jump performance, which would then be unaffected by the high cardiovascular demand.
In conclusion, the current exhaustive jump protocol is an easy and practical way to induce muscular exhaustion of the frontal thighs without the use of any mechanical devices. By combining subjective (i.e., DOMS and RPE) and objective (i.e., CMJ and PPO) parameters, recovery can be investigated without taking any blood samples during a 72 h recovery period. The local post-exercise cryotherapy application can be carried out nearly anywhere and guarantees constant cooling temperatures.