15 college male soccer athletes volunteered to participate into this study. Exclusion criteria included: hypertension, diabetes, cardiovascular risk factors, other any diagnosed diseases, smoking, ingested alcohol, caffeine, nutritional supplements and drugs one week before and throughout the study. Inclusion criteria: 1) 18-24 year; 2) BMI ranged from 18.5 to 23.9 kg/m2; 3) At least 5 years of regular soccer training experience, maximal oxygen uptake over 50ml/kg/min. The study protocol was approved by the Internal Review Board of Beijing Sport University (2020057H). All subjects were informed the aims of the study and were asked to sign an informed consent. One participant dropped out after graded cycling exercise test. 14 athletes completed all the sessions and were included in the data analyses (Table 1).
Table 1
Participant characteristics
Age (year)
|
Height (cm)
|
Weight (kg)
|
Body fat (%)
|
VO2max
|
Wmax
|
Training year (year)
|
20 ± 2
|
178.31 ± 6.36
|
69.58 ± 7.22
|
13.11 ± 3.50
|
55.93 ± 5.36
|
298.54 ± 41.7
|
9 ± 3
|
Note. Values are mean ± SD. VO2max, maximal oxygen uptake; Wmax, maximal power output.
|
Study design
A randomized, double-blind, crossover designed trials was used in this research. There were five laboratory visits, each divided by 7 days. The first visit involved personal information collection, body composition measurement, familiarization with exercise test protocol and performed a graded cycling exercise test (GXT). Second visit, they measured body composition and took sodium pyruvate or maltodextrin (0.1g/kg/d) for 7 days (parallelly and randomly, PYR (n=7), PLA (n=7)). During the third visit, 45-min after the last supplementation, the subjects took a 15-minute resting oxygen uptake test (RO2). Then performed high-intensity interval exercise (HIIE) test to induce metabolic acidosis, and conducted RSE capacity test 10 min after HIIE. Subjects had third round of body composition measurement at fourth visit, those who supplied pyruvate/maltodextrin in the first round were switched to maltodextrin/pyruvate (parallelly and randomly, PYR (n=7), PLA (n=7)). After 1-week, they returned to the laboratory and replicated the test they had done during the third visit. Each subject performed the tests at the same time of day and the same laboratory environment.
Participants arrived in a resting and thoroughly hydrated condition of ≥ 2 h post-prandial, avoid any strenuous exercise and carbonated drinks, alcohol, caffeine 24 h before each exercise test. A 3-day dietary recall was used to measure calorie intake and macronutrient consumption (2 weekdays and 1 weekend). Subjects took a 24-hour recall to measure dietary consumption the day before the first trial, and were asked to replicate the same diet as accurately as possible in subsequent studies. To ensure compliance, participants were expected to ingest the supplement under supervision. Fig. 1 presents a timeline for this study.
Body composition measurements
Height was collected to the nearest 0.1 cm using a calibrated electronic scale (GMCS-SGJ3, Jianmin, Beijing, China). Body composition was assessed 2 h after meal by multi-frequency bioelectrical impedance measurements device (Inbody 230, Biospace, Seoul, Korea).
Graded cycling exercise test
Each subject performed GXT on an electromagnetically braked cycle ergometer custo-med EC 3000e (custo med, Ottobrunn, Germany) to determine peak power (Wmax) and maximum oxygen uptake. Participants adjusted the seat and warmed up for 3 min at 50W. Then, pedal frequency was kept between 75 to 80 rpm, with load increased at 30W per minutes. The standards for exhaustion included: 1) Subjects failed to keep 75rpm for 5 s, voluntary exhaustion; 2) Increase the power load, but VO2 change ≤ 150ml/kg/min; 3) Respiratory exchange rate (VCO2/VO2) ≥ 1.10; 4) Heart rate reached 220-age. VO2peak is the average oxygen consumption 30 s before reaching exhaustion 31. Wmax was calculated as the power of the last completed stage plus the fraction of time spent in the final non-completed stage multiplied by 30 W 32, 33. The rate of perceived exertion (RPE) and heart rate (HR) were measured during the test using the Borg scale (6-20) 34 and Polar V800 (Polar Electro Oy, Oulu, Finland).
Supplementation protocol
Sodium pyruvate (Lianlu industrial Co., Ltd., Shanghai, China) and maltodextrin were randomly packed in capsule A or B that similar in appearance, size and weight. Each participant took 0.1g/kg/d 35 pyruvate or maltodextrin for 7 days (ingested 2 capsules per meal and 1 capsule before sleep for the first 6 days; supplied 60 min prior to exercise test for the 7th day 35). Subjects took capsule A this time were switched to capsule B the next time.
Oxygen uptake test
VO2 was measured breath-by-breath at CXT, rest, during HIIE and 10 min after HIIE using a portable gas analyzer (Cortex Metamax 3B, CORTEX Biophysik, Leipzig, Germany).
RO2 was measured 45-min after last supplementation. Participants take a 15-min break in a sitting position. The RO2 was determined using the average of the last 10 min of data collected 36.
The gas analyzer was calibrated pre-exercise in accordance with the instructions of manufacturer.
HIIE protocol
HIIE was conducted in an electromagnetically braked cycle (Ergoline Ergoselect 100K, Ergoline, Bitz, Germany). During the test, subjects took a warm-up at 60 W for 5 min. HIIE consisted of 4 * 1 min cycling bouts at 110% Wmax. Cadence was constant (90-100 rpm) and were interspersed by 1min rest intervals. Volunteers remained seated on the ergometer to took a 10-min break after finishing the last bout.
RSE test
RSE consisted 6 * 6 s of all out maximal cycling was performed on a mechanically braked cycle ergometer (Monark Ergomedic 894E, Monark, Vansbro, Sweden). Exercise load = weight (kg) × 0.087kp/kg (weight) 37. During the test, participants adjusted the seat and began to fully ride when the staff countdown "3, 2, 1, start". Once cadence reached 110 rpm, the load of ergometers inertial was adjusted to the predetermined load. Subjects keep fully pedaling to complete 6s cycling exercise, encouragement was provided to enable subjects to exert maximum ability. Each sprint with 24 s rest interval 38.
RPP: the highest power output (PP) relative to body mass observed in each 6 s; RAP: the average power output (AP) relative to body mass maintained in each 6 s; Power drop (PD%): the percent of decay of mechanical power during the entire test with respect to peak power, according to the following equation: PD% = [(PP − AP)/PP × 100]. All the parameters were calculated via Monark Anaerobic Testing software (Version: 3.3.0.0, Developed in Co-operation with HUR Labs).
Blood collection and analyses
10 ul of finger-stick capillary blood samples were collected (wiped away the first drop of blood) in a Biosen capillary tube (EKF Diagnostics, Barleben, Germany) at baseline, end of each 110%VO2max bout, 3, 5, 7, 10 min after HIIE and post-RSE. The samples were analyzed using lactate analyzer (Biosen C-Line, EKF Diagnostics, Barleben, Germany) to measure blood lactate concentration.
1ml of blood samples were obtained from ulnar vein at baseline, pre-HIIE, post-HIIE, pre-RSE and post-RSE. The samples were collected in sodium heparin tube and immediately assessed blood pH, HCO3-, BE by blood gas analyzer (Radiometer ABL80, FLEX CO-OX, Willich, Germany).
Estimation of energy contribution
Oxygen uptake: resting oxygen consumption was subtracted from the oxygen consumption obtained during each 110% Wmax bout. Oxidative energy system contribution = total oxygen uptake (L) × 20.92 kJ 39.
Lactate difference before and after each 110% VO2max bout assumed to calculate glycolytic energy contribution. 1 mM of lactate corresponds to 3 ml of oxygen/kg of body mass 39.
Phosphagen energy system contains two sections. First, resting oxygen uptake was subtracted from the oxygen consumption obtained during each 1-min interval. In addition, fast component of excess post-exercise oxygen uptake (EPOC fast) accessed during 6 min of HIIE recovery was adjusted by a bi-exponential model (OriginPro 8.0, OriginLab, Microcal, Massachusetts, USA). EPOC fast was assumed as the product of the amplitude and time constant of the first exponential model 40.
Statistical analyses
A power analysis (Power 1-β = 0.9 and α = 0.05) was performed a priori in G*Power software version 3.1.9.6 (Universitat Kiel, Germany), 12 participants were needed for the present study. Data analyzed were carried out using SPSS, version 22.0. (SPSS Inc. Chicago, IL, USA). The Shapiro-Wilk test was used to verify the assumptions of normality of the data. Non-parametric Kruskal-Wallis test was used to analyze power drop (%). Two-way repeated measures ANOVA was performed to assess the interaction between time (baseline, each bout of HIIE and each sprint of RSE) and the cohort (PYR and PLA). Simple effect analysis was performed for the horizontal comparison of between-group-factors when there was an interaction. Longitudinal comparison of within-group-factors was performed when there was no interaction. Independent samples t-tests were used to measure total, relative energy contribution during HIIE and average PD% during RSE. Values were expressed as mean ± SD or median (P25, P75). The statistical significance level was set at p < 0.05.