Subjects
Eleven men (mean ± SD: age, 22.7 ± 0.9 years; height, 175.7 ± 6.7 cm; body weight, 73.6 ± 10.2 kg; BMI, 23.8 ± 2.7 kg/m2) participated in the present study. None of them was taking part in any regular training program at the start of the experiment (with exercising recreationally once per week). However, all subjects had several years of experience performing strenuous resistance training. The inclusion criteria for subject selection were experience with strenuous resistance training at least a year, no habit of wearing CG in daily sport activities. The subjects were informed about the purpose of the study and the experimental procedures, and they provided a written informed consent. The present study was approved by the Ethics Committee for Human Experiments at Ritsumeikan University, Japan, in accordance with the Helsinki Declaration.
Experimental overview
The present study was performed with a randomized crossover design. The subjects visited the laboratory four times throughout the experimental period. On the first visit, all subjects provided a written informed consent. On the second visit, one-repetition maximum (1RM) for four exercises was measured to determine the weights to be used for each exercise on the experimental days. The subjects also conducted a familiarization session of exercise protocol, consisting of 10 × 6 s all-out sprint separated with 30-s rest between the sprints under 7.5% of each body weight, 10 × 3 sets resistance exercise for four exercises, and 5 × 10 drop jumps (50 jumps in total).
On the third and fourth visits, the subjects completed two experimental trials, either with the use of a CG (CG trial) or without the use of a CG (CON trial) during post-exercise period after performing two repeated bouts of exercise, separated with 4 h of rest (Ex1: 9:00–10:00, Ex2: 14:00–15:00). The CG and CON trials were conducted in a random order separated by a month. Immediately after completing 60 min of each exercise, the subjects in the CG trial changed into a whole-body CG (Recharge; Under Armour, Baltimore, MD) [7, 24]. The pressure levels applied for the present CG were previously reported [25], 11.5 ± 0.6 hPa for thigh and 17.6 ± 1.8 hPa for calf. In the CON trial, the subjects wore a non-CG, identical type of sports wear without specific compression. The appropriate size of the CG for each subject was chosen on the basis of the garment’s instruction manual and involved measurements of the height, chest, waist, and ankle circumferences. The subjects wore the prescribed garments throughout the whole recovery period (4 h after Ex1 and approximately 18 h after Ex2), except during two repeated bouts of exercise (60 min for each exercise), during measurements of exercise performances, blood drawing, and showering at night. Time courses of changes in upper and lower body muscular strength and power, blood metabolites, hormone and cytokine levels, and scores of muscle soreness and fatigue were monitored during 24 h after the onset of Ex1 (Fig. 1).
On the experimental days, all subjects stayed at the same facility located in the university. They spent time by reading books, listening music, or watching DVD. They were allowed to consume water ad libitum. The subjects were given identical lunch (12:00) and dinner (19:00) in both trials. The sleep duration on exercise days was controlled from 23:00 to 07:00.
Strenuous exercise session
Exercise consisted of three different exercises to mimic regular training for improving fitness levels among team sport athletes, including repeated sprint exercise, resistance exercise, and drop jump. We selected this protocol because all exercises are commonly used for daily training on sport fields. For the repeated sprint exercise, the subjects completed 10 × 6 s all-out sprint separated with 30 s rest between the sprints using an electromagnetically braked cycle ergometer (Power Max VIII; Konami Corporation, Tokyo, Japan). The resistance of pedaling was set at 7.5% of each body weight. Resistance exercise consisted of four exercises: three exercises for upper body muscles (chest press, lat pull down, shoulder press) and an exercise for lower limb muscles (bilateral leg press) using weight stack machines (Life Fitness, Ltd., Tokyo, Japan). Each exercise involved 10 repetitions, with five sets for chest press and lat pull down and three sets for shoulder press and bilateral leg press. The resistance was set as 75% of 1RM for each exercise. The subjects rested for 2 min between sets and exercises. Before the training session in each trial, the subjects performed warm-up sets comprising 10 repetitions at 50% of the 1RM and stretching of the major muscle groups targeted by the exercises. For drop jump, the subjects completed 5 × 10 drop jumps (50 jumps in total) from a height of 40 cm. All jumps were performed with placing hands on hips. After landing, they are requested to pause at a squatting position, with hand on hips and knees flexed to approximately 90° and subsequently conducted vertical jump with maximal effort [6, 22]. Each exercise session including repeated sprint exercise, resistance exercise, and drop jump lasted 60 min. The exercise session was repeated twice in the morning (9:00–10:00, Ex1) and afternoon (14:00-15:00, Ex2) under supervision by laboratory staff.
Measurements
Before Ex1 (8:40), immediately after Ex1 (10:00), immediately before Ex2 (14:00, 4 h after Ex1), 4 h after Ex2 (19:00), and 24 h after the onset of Ex1 (9:00), maximal power for bench press, jump performance, blood variables, scores of fatigue, and muscle soreness were evaluated. The repeated sprint ability was also evaluated three times: during Ex1, during Ex2, and at 24 h during post-exercise period (Fig. 1).
Evaluation of repeated sprint ability
To evaluate repeated sprint ability, the subjects performed repeated sprint exercise, comprising 10 × 6 s all-out sprint with a 30-s rest period between sprints. Before the exercise, the subjects completed a standardized warm-up on an electromagnetically braked cycle ergometer (Power Max VIII; Konami Corporation, Tokyo, Japan). The applied load for the repeated sprint test was equivalent to 7.5% of the subjects’ body weight. The mean power outputs during each set of sprint were recorded by a computer (Edge E420, Lenovo, Beijing, China) every 0.1 s using specially designed software (Konami, Tokyo, Japan). The power output decrement (%) was calculated by percentage reduction of power output over the 10 sprints.
Strength measurement
For the indication of muscular power output for upper and lower limb muscles, bench press power output and jump performances were evaluated. Power output for bench press power output during concentric phase (elevating phase) was determined using an accelerometer (Myotest SPORT, Myotest SA, Sion, Switzerland) connective to a bench press bar [25]. After the beep, the subjects completed bench press exercise during concentric (elevating) phase as fast as possible. The weight of the exercise was set equivalent to 40% of 1RM, and mean power output (MPO) during the elevating phase was calculated. The measurement was repeated three times, and the maximal value was adopted.
Jump performance was evaluated using two types of jump tests. For the CMJ test, the subjects performed a maximal vertical jump on a platform (CT-916, Takei Scientific Instruments Co. Ltd., Niigata, Japan) that was connected to a personal computer. Subjects were instructed to perform a maximal jump while placing hands on the lumbar division to eliminate upper limb effects. The vertical jump flight time was recorded. From the flight time, the CMJ height was calculated using the formula [(Jump height (m) = 1/8 (flight time)2 × (the gravity constant)]. The rebound jump (RJ) test was then performed to evaluate stretch shortening ability for lower limb muscles. The subjects were instructed five repeated maximal jumps on a platform with minimum contact time, and the jump height, contact time, and RJ index (jump height/contact time) were calculated [6]. From the obtained results from the five jumps, the average value among three values except the highest and lowest values was adopted for further analysis.
Blood variables
Venous blood samples were obtained from an antecubital vein before Ex1, immediately after Ex1, immediately before Ex2 (4 h after Ex1), 4 h after Ex2, and 24 h after the onset of Ex1 to determine blood glucose and lactate concentrations. Serum creatine kinase (CK), myoglobin (Mb), leptin, and plasma interleukin-6 (IL-6) concentrations were also evaluated before Ex1 and at 24 h after the onset of Ex1. Serum and plasma samples were obtained by centrifuging for 10 min and were stored at −80 °C until analysis. Serum CK and Mb concentrations were measured at a clinical laboratory (SRL Inc., Tokyo, Japan). The intra-assay CVs were 3.4% for CK and 6.0% for Mb measurements. Serum leptin and plasma IL-6 concentrations were measured with enzyme-linked immunosorbent assay (ELISA) using kits from R&D Systems (Minneapolis, MN, USA). The intra-assay CV was 9.5% for leptin and 8.2% for IL-6, respectively.
The blood glucose and lactate concentrations were measured immediately after blood collection using an automatic glucose analyzer (Free Style, Nipro Corporation, Osaka, Japan) and lactate analyzer (Lactate Pro2; Arkray Inc. Kyoto, Japan), respectively.
Scores of fatigue and muscle soreness
Scores of subjective fatigue and vitality were evaluated six times (before Ex1, immediately after Ex1, before Ex2, immediately after Ex2, 4 h after Ex2, 24 h after the onset of Ex1) using a 100-mm visual analogue scale (VAS), where 0 mm represented “no fatigue (or “filled vitality”) at all” and 100 mm represented “unbearable fatigue (or “no vitality at all”)” [21]. At 24 h after the onset of Ex1, muscle soreness was assessed using a 100-mm VAS, where 0 mm represented “no pain at all” and 100 mm represented “unbearable pain”. The subjects were asked to rate the feeling experienced by making the line.
Statistical analysis
Data are expressed as means ± standard deviation (SD). For comparisons of time-course changes in exercise performance, blood variables, and subjective feeling of fatigue, a two-way analysis of variance (ANOVA) with repeated measures was initially applied. When the ANOVA revealed a significant interaction or main effect, a Tukey-Kramer test was performed for post hoc analyses. For comparison of scores of subjective feeling evaluated at 24 h after the onset of Ex1, a paired t test was applied. For all tests, P < 0.05 was considered significant.