Effects of New Zealand Blackcurrant on Athletic Performance and Physiological Stress in Simulated Volleyball Matches

Handgrip strength of both hands was evaluated using a digital dynamometer (T.K.K. 5401 GRIP-D, Takei Scientific Instruments Co., Ltd., Niigata, Japan). During testing, participants maintained a standing position with the shoulder abducted at approximately 20°-30° without rotation, the forearm in a neutral position, and both the elbow and wrist in 0° extension. Participants were instructed to exert maximum effort gripping the handle for 5 seconds.

Handgrip strength tests were conducted before and after the simulated volleyball matches, as well as during the rest interval between the first and second simulated matches. At each time point, two trials were performed for each hand with a 1-minute rest interval between trials, and the maximum value was recorded in kilograms (kg).

Vertical jump performance was analyzed using the My Jump 2 application. Participants started from an upright standing position with the body straight, then performed a rapid countermovement followed immediately by a maximal vertical jump. Each participant performed two trials with a 1-minute rest interval between trials, and the best trial was recorded for analysis.

Agility was evaluated using the T-test with the BlazePod light-based reaction training system (Play Coyotta Ltd., Tel Aviv, Israel), with time recorded in seconds (s).

Course Layout:

Point A served as the start line. Point B was placed 9.14 m directly in front of Point A. Points C and D were placed 4.57 m to the left and right of Point B, respectively. Reaction pods were placed at each point.

Test Procedure:

Timing began upon departure from Point A. Participants were required to touch each pod using their outside hand throughout the trial:

Forward Sprint: Sprint forward from A to B and touch pod B. Left Shuffle: Side-shuffle left to C and touch pod C. Right Shuffle: Side-shuffle right past B to D and touch pod D. Return & Backpedal: Side-shuffle left back to B, touch pod B, then backpedal past A and touch pod A to complete the trial and stop timing.

A designated landing area measuring 1.5 m x 1.5m was set up at a distance of 5 m from the net. The participant stood on a volleyball platform approximately 80 cm high and 1.5 m from the net. The participant was required to toss the ball to an appropriate height (approximately 1 m) and spike it into the designated area. Ball velocity was analyzed and recorded using the Kinovea motion analysis software (Kinovea, open-source video analysis software). Three trials were performed for each test, with a 30-second rest interval between trials.

Blood samples were collected at four different time points (one and a half hours before the start of the volleyball special (B), immediately after the simulated volleyball game (E), after the experiment (24 hours), and after the experiment (48 hours). Changes in blood glucose levels were estimated using blood from the fingertips via an Accu-Chek® Guide blood glucose glucometer (Roche, Mannheim, Germany). Muscle damage biomarkers, including creatine kinase (CK), lactate dehydrogenase (LDH), and uric acid (UA), were measured in the serum. The CK (EC2.7.3.2), LDH (EC 1.1.1.27), and UA (C97792) concentrations were estimated using commercial analytical reagents (Beckman Coulter). An automated clinical chemistry analyzer was used to measure CK and LDH levels on a Beckman Coulter AU5800 (Beckman Coulter Inc., CA, USA).

Blood samples were collected at four different time points (one and a half hours before the start of the volleyball special (B), immediately after the simulated volleyball game (E), after the experiment (24 hours), and after the experiment (48 hours). According to the manufacturer's instructions, the pro-inflammatory cytokine TNF-α was analyzed with a commercial ELISA kit (BioLegend, San Diego, CA). An enzyme immunoassay read The absorbance at 450 nm within 15 minutes (Tecan GENios, A-5082, Austria). Concentrations of C-reactive protein (CRP) were measured using a human ELISA kit (E-80CRP, Immunology Consultants Laboratory, Inc., Newberg, OR, USA). The sample absorbance was read at 450 nm within 30 min.

biomarker used to evaluate total antioxidant capacity. Serum SOD activity is measured using a commercial colorimetric assay kit and read with an ELISA plate reader.Unit of Measure: Units per milliliter (U/mL).

This experiment used a version developed by Swedish psychologist Gunnar Borg, using a scale ranging from 6 to 20. During breaks and after each round of a simulated volleyball match, participants were asked to clearly indicate their RPE (Rate of Perceived Effort) on a paper-based scale. The corresponding level was used to determine the participant's current level of exertion and to record this number.

The VAS is a pain scale developed by Donna Wong and Connie Baker. Six cartoon faces are drawn on a piece of paper. From left to right, they are: no pain (0), a little pain (2), some pain (4), pain (6), very painful (8), and severe pain (10). Scales from 0 to 10 are marked below the faces, as shown in Figure 6. This scale will be used at three time points: immediately after the simulated volleyball match, and 12, 24, 36, and 48 hours after the match. Please clearly indicate the corresponding face and record it according to the number.