High-Intensity Training Improves Exercise Performance in Elite Women Volleyball Players During a Competitive Season

Abstract

Purkhús, E, Krustrup, P, and Mohr, M. High-intensity training improves exercise performance in elite women volleyball players during a competitive season. J Strength Cond Res 30(11): 3066–3072, 2016—Elite women volleyball players (n = 25; mean ± SD: age, 19 ± 5 years; height, 171 ± 7 cm; weight, 63 ± 10 kg) volunteered to participate in the study. They were randomized into a high-intensity training (HIT; n = 13) group and a control (CON; n = 12) group. In addition to the normal team training and games, HIT performed 6–10 × 30-seconds all-out running intervals separated by 3-minute recovery periods 3 times per week during a 4-week in-season period whereas CON only completed the team training sessions and games. Preintervention and postintervention, all players completed the arrowhead agility test (AAT), a repeated sprint test (RST; 5 × 30 meters separated by 25 seconds of recovery), and the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) followed by a-10 minute rest period and the Yo-Yo IR1 test. Mean running distance during HIT in week 1 was 152 ± 4 m and increased (p ≤ 0.05) by 4.6% (159 ± 3 m) in week 4. The AAT performance improved (p ≤ 0.05) by 2.3% (18.87 ± 0.97–18.44 ± 1.06 seconds) and RST by 4.3% postintervention in the HIT group only. Baseline RST fatigue index was 7.0 ± 2.9 and 6.2 ± 5.0% in HIT and CON, respectively, but was lowered (p ≤ 0.05) to 2.7 ± 3.0% posttraining in HIT and remained unaltered in CON (5.5 ± 5.0%). In HIT, Yo-Yo IR2 and Yo-Yo IR1 performance improved by 12.6 and 18.3% postintervention, respectively, with greater (p ≤ 0.05) Yo-yo IR1 change scores than in CON. In conclusion, additional high-intensity in-season training performed as interval running improved agility, repeated sprint ability, and high-intensity intermittent exercise performance in elite women volleyball players.

Introduction

Volleyball began to develop as a sport in the late 19th century and has been an Olympic sport since 1964. The game is often classified as one of the most popular sport activities in the world with more than 900 million participants on a global basis and with competitive tournaments taking place in the 218 National associations.

Volleyball is a high-intensity intermittent sport with frequent explosive movements, where trained players, for example, have been shown to perform ∼115 jumps and 85 hits in a game (²⁷). Volleyball players have been demonstrated to cover ∼1200 and ∼1750 m in total in a 3-set and 4-set game, respectively (³¹), which is markedly less compared with other team sports such as football (²⁸), team handball (³⁴), hockey (²⁵), basketball (³⁵), and ultimate frisbee (¹⁸), where the total distance covered ranges from 5,000 to 12,000 m. Moreover, the exercise periods in volleyball are relatively short, lasting only ∼9 seconds on average interspersed by ∼12-second recovery intervals and display work-to-rest ratios ranging between 1:1.6 and 2.2 (^38,40), which also differs markedly from other team sports.

The physiological loading of a volleyball game is moderate. Cardiovascular loading during an elite volleyball game has been shown to be 75% HRmax on average (⁴⁰), with large interplayer variability. For example, in a beach volley game, average heart rates have been demonstrated to range between 61 and 90% of HRmax with players having heart rates >90% HRmax for one-third of the total playing time (²⁶). Blood lactate concentrations during a volleyball game range between 1.5 and 3 mM (^22,26,31), which is lower than that reported during other classical team sports such as football (³), Australian football (²³), and rugby (³²), indicating a lower glycolytic activity, which may relate to the shorter work periods and smaller pitch area. Moreover, an increase in plasma free fatty acids and catecholamine response has been reported during a game, indicating elevated lipolytic activity (²²).

Fatigue during and toward the end of a game has been shown in football (²⁸), team handball (³⁴), basketball (¹), Australian football (²), and ultimate frisbee (¹⁸). In volleyball, the maximum voluntary contraction performance in both knee extensor and flexors is reported to be impaired by ∼20% after a game and sprint performance is lowered by 3% (²⁶), which comparable with the impairment after a football game (^9,21), despite the markedly lower activity degree and physiological response. In addition, reaction time is shown to deteriorate by 13% during a game (³⁰). Thus, neuromuscular fatigue is likely to occur during a volleyball game in response to the high number of high-intensity and explosive movements.

Most intervention studies performed on volleyball players are focused toward improving technical skills and power output in jumping and spiking (^24,36,37). In contrast, studies are lacking on how to improve the overall fitness level, endurance, agility, and the capacity to perform high-intensity intermittent exercise, which is highly required in a volleyball game. Intensified training has drawn increasing attention by researchers and the sports community during the past decade. For example, high-intensity training (HIT) been shown to increase performance in trained runners (⁶), cyclists (¹⁴), and football players (^11,39) despite marked reductions in training volume. Moreover, additional HIT is demonstrated to improve performance in elite athletes (¹³). However, it is unknown how additional HIT affects performance in elite volleyball players. Finally, the most studies applying HIT regimes have used male participants, and to our knowledge no study has investigated the effect of in-season additional HIT in elite women team sports athletes. Therefore, scientific data are warranted describing the effects of additional HIT in competitive women volleyball players, which may provide valuable information on training strategies for coaches in the sport.

Thus, the aim of the present study was to examine the effect of 4 weeks of in-season additional HIT on agility, repeated sprint ability, and high-intensity intermittent exercise performance in elite women volleyball players. We hypothesized that additional in-season HIT will improve agility, repeated sprint ability, and high-intensity intermittent exercise performance.

Methods

Experimental Approach to the Problem

The study design is a randomized controlled trial, where subjects were randomized into 2 groups; a HIT group (n = 13) and a control group (CON; n = 12). The randomization was team specific, so that there were equal number of players from each of the 4 participating teams in the HIT and CON groups. The HIT was assigned to carry out 3 weekly HIT in addition to the normal team training and match-play over a period lasting 4 weeks, whereas CON only took part in the normal team training and match-play. Before and after the intervention period, the subjects performed a number of high-intensity performance tests to evaluate the effect of the training intervention.

Subjects

A total of 25 elite women volleyball players participated in the study (Table 1). They were all competing in the top volleyball league in the Faroe Islands and represented 4 different teams being ranked in the top, middle, and bottom of the league competition. All teams in the league were approached to participate in the study with the inclusion criteria that the players were regular first team members and that they had been free of injuries for the past 4 weeks leading up to the study. The original sample consisted of 43 players who performed the pretesting procedure. However, 18 dropped out due to the coaches perceiving the intervention as a disturbing element (n = 14) and because of injuries (n = 4), which resulted in the final sample being 25 players. Four of the players were regular national team players, whereas the participating players had on average 9 years (range: 5–22 years) of continuous volleyball experience. In a normal week, the participating players had 5 normal training sessions including a game. One of the training sessions was a resistance (strength) training session performed in a gym (Table 2).

Table 1.: Subject characteristics.*†

Table 2.: Overview of a representative weekly program during the intervention period.*

Before commencement of the study, the subjects were informed of the benefits and risks of the investigation and gave their written informed consent. Parental signed consent was obtained for the 3 players who were <18 years (see age range in Table 1). The study conforms to the code of ethics of the Declaration of Helsinki and was approved and performed in compliance with the human subject guidelines of the Ethics Committee at the University of the Faroe Islands.

Procedures

Four performance tests were conducted. (a) The arrowhead agility test (AAT), (b) a repeated sprint test (RST), (c) the Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1) and (d) Yo-Yo IR2. All tests were performed on an indoor team handball court.

The AAT test examines speed, explosion power, and rapid changes of direction while sprinting. Markers are placed in 3 sets and form the shape of an arrowhead (see ^{Ref. (4)}). The player runs through the start markers, through the middle markers (10-m linear run), then turns left/right through the side markers (5-m run to the side), through the marker at the top (5 m from the middle marker), and then back through the start markers (15-m linear run). The aim for the player is to complete the test as fast as possible. One running bout is performed to the left and one to the right separated by 2-minute recovery (⁴). The result of the test is the total time to complete both the running bouts. The AAT test has been demonstrated to have a high reproducibility (coefficient of variation [CV] = <1%; Mohr, July 2015, unpublished data).

The RST comprised 5 × 30-m linear sprints separated by 25-seconds active recovery during which the subjects jogged back to the starting line. The time to complete each sprint was determined by wireless infrared timing gates (Eleiko Sport, Halmstad, Sweden) as previously described (⁴). Before the sprint tests, a standardized warm-up led by the coach was completed. The final results of the test are the time of the fastest sprint (peak sprint ability) and the mean sprint time of all 5 sprints (repeated sprint ability). A fatigue index (FI) was calculated as the percentage difference between the first and the fifth sprint. The RST performance has been demonstrated to have a high reproducibility (CV = 0.8%; (¹⁷)).

The Yo-Yo IR2 and IR1 tests consisted of 2 × 20-m shuttle runs, gradually increasing through the test levels and signaled by audio beeps (⁴). Before the Yo-Yo IR2 test, the subjects performed a standardized warm-up as described by Krustrup et al. (²⁰), whereas the Yo-Yo IR1 test was performed after 10-minute of recovery from the Yo-Yo IR2 test. Between each running bout in Yo-Yo IR2 and IR1 tests, participants had a 10-seconds active recovery period comprising 2 × 5 m jogs. When the subjects failed twice to reach the finish line in time before the audio beep, the level achieved was recorded and used to calculate the distance covered. The Yo-Yo IR2 and IR1 tests have been shown to have a test-retest reproducibility (CV) of 9 and 5% (⁷).

All participants performed pretests of all tests 7–10 days before the baseline tests to familiarize them with the testing procedure as described by Bangsbo and Mohr (⁴). The baseline tests and postintervention tests were performed on 2 different days with at least 48–72 hours recovery between tests. The AAT and RST were performed on the first day after a standardized warm-up as described by Bangsbo and Mohr (⁴) and the 2 Yo-Yo IR tests were performed the other day. The Yo-Yo IR2 test lasted only 3–6 minutes for the respective athletes, therefore, we completed the Yo-Yo IR1 test 10 minutes after the Yo-Yo IR2 test, to study the effect of the training intervention on prolonged high-intensity intermittent exercise.

The final tests were performed after 4 weeks of training, between 2 and 5 days after the last HIT session. To minimize the risk of errors, the procedure of the postintervention tests was the same as the baseline tests. The AAT and RST were performed on one day and Yo-Yo IR 2 and Yo-Yo IR 1 48–72 hours later under same conditions as the baseline tests. The pretest and posttest were performed on the same time of the day ± 1 hour. Participants were advised to eat a standardized meal 2 hours before testing to be fully hydrated and to avoid consuming alcohol the day before testing and items containing caffeine on the day of testing.

The training intervention was based on the principals of speed endurance production training (^15,16,29), where all-out running was performed in ∼30-second intervals separated by 3-minute periods of recovery (⁵).

The intervention period lasted 4 weeks. The athletes continued their usual volleyball practice 4 times a week including a game with 1 session being resistance training in a gym (Table 2) while the HIT group additionally performed speed endurance training 2.9 ± 0.2 times a week (Table 3). The first week they performed 6 × 30-second of all-out sprinting with 3-minute recovery. The second and the third week they carried out 8 × 30-second runs, whereas in the fourth week they performed 10 × 30-second runs. After each sprint, the distance was measured and noted to report improvements in training effort during the intervention period. The reason for the gradually increase in repetitions was to ensure a progressive loading of the players. Mean running distance improved from 152 ± 14 to 159 ± 11 m (4.4%). The range of running distance per week increased from 150–155 ± 14 to 158–161 ± 15 m (Table 3). The HIT was mostly carried out immediately after 1.5–2.0 hours of volleyball training.

Table 3.: Distance covered during the training intervention in high-intensity training.*

The HIT was performed on an outdoor running track (400 m), on an indoor team handball field (40 × 20 m), and on an outdoor artificial grass football field (100 × 60 m).

Statistical Analyses

Values are given as mean ± SD. Differences in test performance before and after training intervention were tested using paired t-tests, whereas differences between the training interventions (absolute and change score values) were tested using unpaired t-tests. Differences in distance covered during training over the 4 weeks were tested using a one-way analysis of variance with repeated measurements. A significance level of 0.05 was chosen.

Results

Agility

The AAT performance improved (p ≤ 0.05) in HIT postintervention compared with preintervention period (18.87 ± 0.97 vs. 18.44 ± 1.06 seconds; Figure 1). The mean overall improvement in time was 2.3%. No changes were observed in CON.

Figure 1.: Performance in the Arrowhead agility test (AAT) before and after the training intervention in the high-intensity training (HIT) and the control (CON) groups. The bars show the average test scores and the symbols the individual responses. *Significant difference between pretraining and posttraining. Significant level, p ≤ 0.05.

Repeated Sprint Ability

In HIT, mean sprint times in RST were 4.3% better (5.40 ± 0.24 vs. 5.64 ± 0.29 s; p ≤ 0.05; Figure 2A) postintervention compared with preintervention. No significant changes were observed in CON (5.46 ± 0.38 vs. 5.47 ± 0.39 seconds; Figure 2A). Preintervention peak 30-m sprint performance was 5.19 ± 0.33 and 5.36 ± 0.25 seconds in HIT and CON, respectively, and was unaltered postintervention (5.25 ± 0.41 and 5.25 ± 0.26 seconds, respectively).

Figure 2.: Performance (average time) in the repeated sprint test (RST) (A) and the fatigue index (B) before and after the training intervention in the high-intensity training (HIT) and the control (CON) groups. The bars show the average test scores and the symbols the individual responses. *Significant difference between pretraining and posttraining. #Significant difference compared with CON. Significant level, p ≤ 0.05.

In HIT, FI was lower (p ≤ 0.05) postintervention compared with preintervention (2.7 ± 3.1 vs. 7.0 ± 2.9%), whereas there was no change in CON (6.2 ± 5.0 vs. 5.5 ± 5.3%; Figure 2B). In HIT, the FI was lower (p ≤ 0.05) postintervention compared with CON (Figure 2B).

Yo-Yo Intermittent Recovery Test

In HIT, Yo-Yo IR2 performance was 12.6% better postintervention compared with preintervention (191 ± 43 vs. 215 ± 32 m; p ≤ 0.05), whereas there was no significant change in CON (193 ± 62 vs. 204 ± 63 m; p > 0.05; Figure 3A). Preintervention Yo-Yo IR1 performance was better in HIT than in CON (Figure 3B). However, in HIT, Yo-Yo IR1 performance increased by 18.3% (658 ± 198 vs. 556 ± 206m; p ≤ 0.05) postintervention compared with preintervention with no change in CON (Figure 3B). The intervention induced Yo-Yo IR1 change score was greater (STATS) in HIT (p ≤ 0.05) than in CON (Figure 3B).

Figure 3.: Performance in the Yo-Yo intermittent recovery test, level 2 (Yo-Yo IR2) (A) and level 1 (Yo-Yo IR1) (B) before and after the training intervention in the high-intensity training (HIT) and the control (CON) groups. The bars show the average test scores and the symbols the individual responses. *Significant difference between pretraining and posttraining. #Significant difference compared with CON. Significant level, p ≤ 0.05.

Discussion

The present study is the first to examine the effect of additional HIT during the season in elite women volleyball players. The major findings verify the hypothesis that inclusion of HIT 3 times per week in a 4-week period improves agility, repeated sprint ability, and high-intensity intermittent exercise performance markedly. Thus, the physical performance level of elite women volleyball players can be optimized during the competitive season by inclusion of additional HIT.

In the present study, agility improved by 2.3%, whereas peak 30-second linear sprint performance was unaltered after the training intervention. Agility is an important component of high-intensity performance in team sports and includes variables such as acceleration, decelerations, and explosive strength capacity during directional changes (⁴), all of which are important parameters in competitive volleyball games (^37,38,40). The finding of no change in peak sprinting ability in a 30-m linear sprint performance after speed endurance training is supported by other studies applying a similar training strategy (²⁹). The different training responses in the speed and agility tests also demonstrates that the AAT evaluates different physical variables than the linear speed test and may be used in athlete populations such as competitive volleyball players. Moreover, the enhanced agility in the high-intensity group seems to be related to improvement in acceleration/deceleration and directional changes rather than peak running speed, which may be variables of higher relevancy for volleyball players.

Repeated sprint ability was ∼4% higher in the HIT group, which is confirmed by others applying intensified training for normally trained (²⁹) and trained soccer players (¹¹). Moreover, a very large improvement (∼60%) was observed in the FI during the RST, which is supported by an increase of similar magnitude in normally trained men after 8 weeks of speed endurance training (²⁹). Thus, additional high-intensity intermittent training carried out during the competitive season markedly facilitates fatigue resistance during repeated intense actions, which is likely to be highly important in an intense intermittent sport such as volleyball (^38,40). In the present study, no physiological measurements were obtained, but several studies during the last decade have shown very large effects on muscle oxidative capacity (^8,12,33), muscle ion transports (^29,39), type IIx muscle fiber area (¹⁵), and muscle oxygen uptake kinetics (¹⁹) after HIT, which all are suggested to affect repeated sprint performance.

For the first time, the Yo-Yo IR2 and IR1 tests were carried out on the same day separated by a 10-minute recovery period to study the effect of the training intervention on a more prolonged period of high-intensity intermittent training. The HIT improved total distance covered in the Yo-Yo IR tests by 17% compared with pretraining resulting in the total score being ∼30% higher than in the control group. A limitation in the study is that the HIT group had higher Yo-Yo IR1 scores than CON before the intervention. However, HIT had an improvement in Yo-Yo IR1 performance posttraining despite running ∼13% longer in the Yo-Yo IR2 test only 10 minutes preceding the Yo-Yo IR1 test, whereas no change occurred in CON in neither Yo-Yo IR2 nor Yo-Yo IR1 performance over the intervention period. Thus, the addition of in-season speed endurance training caused marked positive adaptations in the ability to perform high-intensity intermittent work taxing both aerobic and anaerobic energy systems (⁷). Several studies have used the Yo-Yo IR tests as performance measure in relation to high-intensity intermittent exercise capacity after similar intense training regimes (^16,29,39) in various male subject groups using training interventions lasting 2–8 weeks. Studies have shown gender-specific responses to high-intensity intermittent exercise, which questions whether men and women differ in relation to adaptability to high-intensity exercise training (¹⁰). However, the present study provides a similar adaptation pattern and magnitude as observed in the above-mentioned training studied, indicating that women team sports athletes display similar responsiveness to high-intensity intermittent training regimes as previously demonstrated in men.

All the applied test responses demonstrated large intersubject variability, which is a common finding in exercise training intervention studies applying HIT regimes (^{6,8,11–14,16}). It is unknown why individuals display these types of individual responses, but it may be associated with the preintervention fitness level or age. Therefore, we correlated the age and fitness level of the subjects in the HIT group before the training intervention to the change score in performance, but no correlation was present suggesting an effect of high and low responders to HIT.

Limited scientific research has currently been conducted on training and testing of competitive volleyball players. Moreover, detailed analyses of movement profiles in games are sparse. Therefore, a volleyball-specific testing battery is yet to be developed and validated. Thus, it is unknown if the training-induced performance improvements in agility, repeated sprint ability, and Yo-Yo IR performance can be transferred to volleyball-specific movements and competitive game performance. Future research should aim at providing data on these aspects, as well as on the effect of HIT performed as volleyball-specific movements.

In conclusion, the findings of the present study verifies the hypothesis that 4 weeks of in-season additional HIT carried out as running markedly improved agility, repeated sprint ability, and high-intensity intermittent exercise performance in elite women volleyball players. Thus, HIT strategies are suggested to be incorporated in the physical preparation of competitive volleyball athletes.

Practical Applications

The study showed that after 4 weeks of high-intensity intermittent training performed 2–3 times per week in conjunction with the normal training in competitive women volleyball players, great improvement was observed in agility, repeated sprint ability, and high-intensity intermittent exercise capacity. Volleyball is played on a relatively small court compared with most other team sports. Therefore, it may be challenging to conduct HIT such as speed endurance training during conventional volleyball practice. The findings of great improvements in physical capacity after only 4 weeks of additional speed endurance training suggests that volleyball coaches should aim at intensifying their training with inclusion of, for example, speed endurance training. These types of additional in-season HIT protocols lasting only a few weeks could be included in periods leading up to international competitions, for example, for national team players. Moreover, it appears from the present study that the AAT combined with RST and the Yo-Yo IR tests are testing procedures that may be applied in competitive volleyball players to evaluate the effects of training.