In this study, the investigators will examine the effect of cold-water immersion (CWI) on objective and subjective recovery metrics, as well as simple performance metrics, in National Collegiate Athletics Association (NCAA) Division I Men's and Women's Volleyball players, Men's Football players, and Men's and Women's Cross Country runners. This is a cohort cross-over study that will take place over the course of four weeks during an intensive training cycle. Participants will wear a WHOOP monitoring device on their wrists at all times during the study period. The two-week intervention will consist of ten minutes of CWI to take place within one hour of the completion of the last training session of the day. The target water temperature will be 55 degrees Fahrenheit, and each participant will complete five sessions of CWI per week (for a total of ten sessions over the two-week intervention phase). Objective recovery measures will include heart rate variability, resting heart rate, total sleep time, slow wave sleep time, sleep consistency, blood oxygenation, and nocturnal skin temperature, all of which will be collected continuously by the WHOOP monitoring device. Subjective recovery measures will include three surveys to be completed daily, including the Likert Scale of Muscle Soreness, the Total Quality Recovery Scale, and the Single-Item Sleep Questionnaire. Performance measures will include a counter-movement jump to be completed two times per week, an isometric mid-thigh pull to be completed once per week, and a drop jump to be completed once per week. These outcome measures will similarly be collected during the two-week control period, during which participants will not have access to CWI following training sessions.

This is a cohort cross-over design that will take place over four weeks during an intensive training cycle. The study population will be randomized into two cohorts. The first cohort will begin with the control phase and then transition to the intervention phase. The second cohort will begin with the intervention phase and then transition to the control phase.

Control phase:

Participants will complete normal training sessions over a 14-day period and will not have access to cold water immersion (CWI) during this time.

Intervention phase:

Participants will complete normal training sessions over a 14-day period. They will complete a session of CWI within one hour of finishing the last training session of the day. CWI will consist of ten minutes of submersion to the neck in a cold-water tub with a target temperature of 55 degrees Fahrenheit (daily temperatures will be recorded at the time of each session). The acceptable range for the CWI protocol will be from 53-57 degrees Fahrenheit. The immersion process will not be completed if the temperature of the water is outside of this range. Participants will complete five sessions per week, with a total of 10 sessions to be completed over the 14-day intervention.

Participants will wear a WHOOP 4.0 wrist device throughout the entire four-week study period to collect continuous biometric data and to monitor sleep patterns overnight. Athletic performance testing will consist of a counter-movement jump completed two times per week, an isometric mid-thigh pull completed one time per week, and a drop jump completed one time per week. Participants will complete three surveys daily over the four-week period. Participants will be aware of their performance testing metrics and physiologic measures as reported in the WHOOP app.

Physiological Measures:

Biometric Monitoring:

Participants will be asked to wear a WHOOP 4.0 wrist device throughout the entirety of the study period. This device will provide continuous biometric data including resting heart rate, exertional heart rate, heart rate variability, respiratory rate, blood oxygenation, and skin temperature.

Sleep Monitoring:

Participants will be asked to wear a WHOOP 4.0 wrist device throughout the entirety of the study period, which will provide detailed data regarding sleep quantity, quality, consistency, and efficiency. It will also provide information about the time spent in each phase of sleep (light, REM, slow wave [deep], and awake) and respiratory rate throughout sleep.

Athletic Performance Testing:

Counter-movement jump:

The Counter-movement Jump (CMJ) is a vertical jump test performed by having an athlete quickly squat on a force plate to a self-selected depth and then jump as high as possible. It is primarily used for monitoring sports performance, inter-limb asymmetries, neuromuscular fatigue, and the effectiveness of different training programs.

Isometric mid-thigh pull:

The Isometric Mid-Thigh Pull (IMTP) is performed on a dual force plate system with a barbell locked at mid-thigh height, with the athlete attempting to produce as much force as possible as quickly as possible. The test requires an individual to pull on a fixed barbell while standing on the force plate system with a maximal effort for 3-5 seconds. It has been used in studies that evaluated the effects of resistance training programs on maximum strength development, the acute ergogenic effects of supplements on strength (e.g., sodium bicarbonate, caffeine), and the influence of motor learning strategies on maximum force production. Additionally, the isometric mid-thigh pull test is also used to assess fatigue and recovery from exercise and competition.

Drop jump:

The drop jump is a fitness test of leg strength and power which requires the athlete to "drop off" a box and immediately jump as high as they can. The athlete stands on a box, adjacent to the force plate. The athlete then drops down off the box onto the force plate, bending the knees on landing, then immediately performs a maximal vertical jump. The athlete jumps vertically as high as possible, and lands back on the mat with both feet landing at the same time. This test is designed to assess average power and reactive strength.

Perceptual Measure and Questionnaires:

Single-Item Sleep Quality Scale (SISQ):

Participants will be asked to complete the single-item sleep quality scale daily. This survey has been validated against the Pittsburgh Sleep Quality Index (PSQI) for assessment of subjective sleep quality. Participants will rate the quality of their sleep on a scale of 1-10. The survey will consist of the following prompt: "Please think about the quality of the participant's sleep overall, such as how many hours of sleep the participant got, how easily the participant fell asleep, how often the participant woke up during the night (except to go to the bathroom), how often the participant woke up earlier than the participant had to in the morning, and how refreshing the participant's sleep was. Over the past seven days, how would the participant rate the participant's sleep quality overall? (Mark only one box from 0-10, with 0 being terrible, 1-3 being poor, 4-6 being fair, 7-9 being good, and 10 being excellent)."

Total Quality Recovery Scale (TQR):

Participants will be asked to complete this survey daily. This tool is an overall measure of perception of recovery on a 6-20 point scale, estimating the perception of recovery daily to detect the current form of athletes and to monitor short-lived emotional changes. The TQR scale is similar to the perceived exertion scale and is used as a means to measure psycho-physiological recovery. A score for the TQR is ideal at a value of 20, and a score of 13 is considered the minimum score; any scores below this indicate that recovery is incomplete.

Likert Scale of Muscle Soreness (LSMS):

Participants will be asked to complete this survey daily. This tool is a measure of lower limb muscle soreness and has been validated against the Visual Analog Scale in athletes. The survey assesses subjective ratings of lower body soreness (quadriceps, hamstrings) ranging from 0-6 (0 = complete absence of pain; 1 = light pain felt only when touched/a vague ache; 2 = moderate pain felt only when touched/a slight persistent pain; 3 = light pain when walking up or down stairs; 4 = light pain when walking on a flat surface/painful; 5 = moderate pain, stiffness, or weakness when walking/very painful; and 6 = severe pain that limits my ability to move).

Medical Equipment:

In-ground Cold Plunge Pool:

The investigators will be utilizing the in-ground cold plunge pools located in the UCLA athletic training rooms. The water in the pool is chlorinated and checked and maintained at a 1.0-1.2 ppm by a CPO (certified pool operator) daily. There is a recirculating sand/silicate filtration system. All study participants will be required to shower prior to use and follow all Occupational Safety and Health Administration (OsHA protocols, in line with the Campus Department of Health and Safety. Additionally, the pools have a UV sanitization system. There are grab rails on all steps/stairs, as well as non-skid grips on steps to reduce the risk of slips and falls.

Inclusion Criteria:

• Male and female student-athletes aged 18 years or older
• Currently enrolled at UCLA and participating in the following National Collegiate Athletics Association (NCAA) Varsity sports: Men's and Women's Volleyball, Football, Men's and Women's Cross Country.

Exclusion Criteria:

• Must meet above inclusion criteria.
• Unable to complete the required physical testing due to injury or other impairment.
• Age less than 18 years old at time of enrollemnt
• Open wounds or broken skin
• History of hypersensitivity to cold, including but not limited to Raynaud's phenomenon, cold urticaria, cryoglobulinemia, and paroxysmal cold hemoglobinuria
• Under the influence of drugs or alcohol.

Collected data will be stored and managed using REDCap secure web-based database management system. Any personally identifiable information will be coded.