International Journal of Sports Physiology and Performance, 2014, 9, 1033-1039 http://dx.doi.org/10.1123/ijspp.2013-0258 © 2014 Human Kinetics, Inc.

www.IJSPP-Journal.com ORIGINAL INVESTIGATION

Energetics of Shuttle Runs: The Effects of Distance and Change of Direction Paola Zamparo, Ivan Zadro, Stefano Lazzer, Marco Beato, and Luigino Sepulcri Shuttle runs can be used to study the physiological responses in sports (such as basketball) characterized by sprints (accelerations/decelerations) and changes of direction. Purpose: To determine the energy cost (C) of shuttle runs with different turning angles and over different distances (with different acceleration/deceleration patterns). Methods: Nine basketball players were asked to complete 6 intermittent tests over different distances (5, 10, 25 m) and with different changes of direction (180° at 5 and 25 m; 0°, 45°, 90°, and 180° at 10 m) at maximal speed (v ≈ 4.5 m/s), each composed by 10 shuttle runs of 10-s duration and 30-s recovery; during these runs oxygen uptake (VO2), blood lactate (Lab), and C were determined. Results: For a given shuttle distance (10 m) no major differences where observed in VO2 (~33 mL · min–1 · kg–1), Lab (~3.75 mM), and C (~21.2 J · m–1 · kg–1) when the shuttle runs were performed with different turning angles. For a given turning angle (180°), VO2 and Lab were found to increase with the distance covered (VO2 from 26 to 35 mL · min–1 · kg–1; Lab from 0.7 to 7.6 mM) while C was found to decrease with it (from 29.9 to 10.6 J · m–1 · kg–1); the relationship between C and d (m) is well described by C = 92.99 × d0.656, R2 = .971. Conclusions: The metabolic demands of shuttle tests run at maximal speeds can be estimated based on the running distance, while the turning angle plays a minor role in determining C. Keywords: basketball, shuttle test, running economy, intermittent exercise Basketball is a team sport played by both male and female athletes in over 200 countries.1 This sport is characterized by an “intermittent game model” where players perform specific activities such as jumps, changes of direction, and sprints.2–7 By means of time–motion analysis it was shown that players perform about 1000 movements (jogs, runs, sprints, and shuffles) during a game and spend from 6% to 20% of the time in highintensity activities during the match.2–4,6 In addition, these movements are very frequent, with a change of action (and of direction) every 2 seconds.2 The physiological response of these activities is difficult to determine, and, indeed, the data reported in the literature are mainly of heart rate and blood lactate concentration during the match.2–4,6,8 However, these measures only provide an indirect estimate of the energy demands during a basketball competition.9 Shuttle runs are a type of intermittent exercise that can be used to study the physiological responses of these high-intensity activities, since these running conditions (with changes of direction, accelerations, and decelerations) are closer to those observed during a match than continuous running is. However, the energy expenditure during a single shuttle run does not reach a steady state and thus cannot be easily determined; the studies on this topic are indeed limited and refer essentially to shuttles of 10 to 20 m and to changes of direction of 180°.7,10 These studies indicate that the cost of locomotion (C, the metabolic energy needed to cover the shuttle distance) is larger than that of linear running at constant speed; C is larger the higher the running speed and C is larger the shorter the shuttle distance.10 The cost of decelerations and accelerations imposes larger physiological Zamparo and Beato are with the Dept of Neurological and Movement Sciences, University of Verona, Verona, Italy. Zadro, Lazzer, and Sepulcri are with the Dept of Medical and Biological Sciences, University of Udine, Udine, Italy. Address author correspondence to Paola Zamparo at paola. [email protected].

demands on athletes than linear running at constant speed, and the mechanical determinants of this “extra cost” were recently investigated by Minetti et al11,12 in walking and running while adopting acceleration/deceleration cycles (eg, at oscillating speed). The energy expenditure during shuttle runs/sprint running can be estimated based on indirect approaches (eg, from data of speed and acceleration that can be derived by match or video analysis10,13,14). However, as shown by Buglione and di Prampero10 these methods give reasonable estimates of C only for long shuttle distances (eg, 20 m, like those generally used in team sports such as soccer and rugby), whereas they tend to underestimate C in shorter shuttle runs (eg, 10 m). This depends on the assumptions on which these calculations are made (eg, that accelerated running on flat terrain is similar to running uphill at an “equivalent slope”13); the reader is referred to the Buglione and di Prampero10 article for further details. As shown by Scanlan et al9 (in elite and subelite basketball players), the mean distances covered in jogging, running, and sprinting during a basketball match (live time) is shorter than 10 m: about 2.5 m jogging, 6 m running, and 4 to 9 m sprinting in elite and subelite players. Thus, the indirect methods proposed in the literature10 cannot be applied in this team sport, where, due to the limited space available in the game field, shorter shuttles are more common. Finally, as indicated previously, the energy expenditure of shuttle runs was measured with changes of direction of 180° only.7,10 Even if there are some studies in the literature that address the biomechanical aspects of the change of direction,15,16 the effect of different turning angles on the metabolic expenditure of shuttle runs, to our knowledge, has not been investigated. Based on these considerations, the aims of this study were (1) to investigate the metabolic requirements of shuttle runs (at a given change of direction: 180°) over different distances (5, 10, and 25 m), extending the data reported so far in the literature (10 and 20 m)10 to 1033

1034  Zamparo et al

shorter (5 m, more common in a basketball competition) and longer distances (25 m); (2) to investigate the metabolic requirements of shuttle runs (over a given distance: 10 m) with different changes of direction (0°, 45°, 90°, and 180°), extending the data reported so far in the literature (180°) to more acute (45° and 90°) and obtuse (no change of direction) turning angles; and (3) to propose a method to estimate the metabolic requirements of shuttle runs over the 5-m distance based on data/calculations reported/proposed by Buglione and di Prampero.10

Methods

Downloaded by University of Exeter on 09/25/16, Volume 9, Article Number 6

Subjects The experiments were performed on 9 male basketball players whose principal anthropometric and physiological characteristics are reported in Table 1. All players were recruited from the Snaidero Basket junior team (Italian basketball, league A). An example of their training schedule (120 min of technical and tactical practice, 3 times per week) is given by Zadro et al.7 Before the study, the purpose and objectives of the research were carefully explained to each individual, and written informed consent was obtained from all adolescents and their parents. The study conformed to the standards set by the Declaration of Helsinki, and the local institutional review board approved the procedures.

Experimental Protocol In a recent study we proposed a protocol of intermittent exercise to train young basketball players,7 showing that our training program was effective in reducing energy expenditure and blood lactate accumulation during shuttle runs; these runs lasted 10 seconds with 30 seconds recovery (standing) in between. The total distance covered was about 40 m (20 m before and 20 m after the turn; this is generally referred as a 20-m shuttle) and the change of direction Table 1  Anthropometric Characteristics of the Players and Physiological Data Obtained From the Incremental Test Characteristic

Measure

Age (y)

15.0 ± 0.5

Body mass (kg)

79.8 ± 6.4

Height (m)

1.88 ± 0.08

Body-mass index VO2max (mL ·

(kg/m2)

min–1

·

kg–1)

22.6 ± 1.2 53.7 ± 2.9

Maximal heart rate (beats/min)

189 ± 4.2

Oxygen uptake at VT (% of VO2max)

84.0 ± 2.9

Heart rate at VT (% of HRmax)

91.0 ± 2.9

CLR (J · m–1 · kg–1)

3.97 ± 0.34

Speed at VT (m/s)

4.00 ± 0.20

Speed at VO2max (m/s)

4.51 ± 0.16

vi (m/s)

4.80 ± 0.24

Abbreviations: VO2max: maximal oxygen uptake; VT, ventilatory threshold; HRmax, maximal heart rate; CLR, net energy cost of constant linear running; vi, intermittent speed, corresponding to 120% of speed at VT.

was of 180°. A basketball match can be considered high-intensity intermittent exercise, but, during a game, basketball players cover shorter distances and use different changes of direction; thus, we wanted to test the effect of these parameters on the energetics of shuttle runs. We used the same experimental protocol validated in the previous study: an incremental test to determine the intensity of exercise (the shuttle speed) for each player and a series of shuttle runs over different distances and with different changes of direction. With this approach we would like to give coaches a framework to plan an appropriate training program (by showing the relationship between C and shuttle speed, shuttle distance, and turning angle), as well as to provide data to be used in match analysis to assess the energy requirements during a basketball match.

Physiological Measures Incremental Test.  Maximal oxygen uptake (VO2max) was deter-

mined by means of an incremental test on a treadmill (Saturn, HP Cosmos, Germany) with increments of 0.5 km/h every 30 seconds (at an incline of 1°) until exhaustion. Before beginning the test, subjects were familiarized with the equipment and the procedures. At the beginning of this test, 4 minutes of data were obtained with the subjects running at 10 km/h to determine the oxygen consumption at submaximal speed (VO2submax) and hence the energy cost of linear running. During these experiments, heart rate (HR), oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), and respiratory-exchange ratio (RER) were determined on a breathby-breath basis by means of a previously calibrated metabolimeter (Quark b2, Cosmed, Italy). Ventilatory threshold was determined by means of the V-method, as originally proposed by Wasserman et al.17 At the end of the incremental test a blood sample was obtained from the earlobe at the third to fifth minute of recovery to determine blood lactate concentration (Lab) by means of a portable lactate analyzer (Lactate Pro LT 1710, Arkray, Japan). The following parameters were thus obtained: • VO2max and the speed at which VO2max was reached (vmax). • VO2, HR, and speed at the ventilatory threshold (VO2thr, HRthr, and vthr). • vi (a speed corresponding to 120% of vthr); as indicated by Zadro et al7 this exercise intensity is sufficient to induce training adaptations but not too high to induce substantial lactate accumulation. • The net energy cost of linear running from the ratio of net VO2 to the speed (10 km/h): CLR = VO2net/v. In turn, VO2net was calculated as VO2submax – VO2rest, where VO2submax is the VO2 measured when running for 4 minutes at 10 km/h and VO2rest is the oxygen uptake measured while standing on the treadmill for 5 minutes before the incremental test. CLR was expressed in J · m–1 · kg–1 using an energy equivalent of 20.9 J/mL O2. Shuttle Tests.  The participants were asked to perform a series of 10 shuttle runs over different distances and with different changes of direction (see Table 2). Shuttle runs were performed over the distances of 5, 10, and 25 m (eg, in these shuttles the total distance covered was 10, 20, and 50 m, respectively, half of it covered before the change of direction and half of it after it), with a 180° change of direction, at an average speed equal to vi. The shuttle run over the 10-m distance was repeated with no change of direction (0°) and with changes of 45° and 90°, at an average speed equal to vi. In the

Energetics of Shuttle Runs   1035

Table 2  Schematic Representation of the Experimental Protocol

Downloaded by University of Exeter on 09/25/16, Volume 9, Article Number 6

Shuttle distance (m)

Change of direction (°)

5

180

25

180

10

180

10

90

10

45

10

0

former case (no change of direction) the subjects had to stop after the first 10 m and then resume running (as quickly as possible, as during the other changes of direction) in the same direction for the remaining 10 m. During the experiments an acoustic device helped the players maintain the selected running speed (vi), and the actual speed attained during each run was measured by means of a photocell system (Racetime 2, Microgate system, Italy). Each run was followed by 30 seconds of passive (standing) recovery. The intermittent test lasted about 6 minutes. Before the beginning of the test, subjects were familiarized with the equipment and procedures, and 5 minutes of metabolic data were obtained with the subjects standing to determine resting metabolic rate. During this test HR, VO2, VCO2, VE, and RER were collected on a breath-by-breath basis by means of a previously calibrated portable metabolimeter (K4b2, Cosmed, Italy). At the end of the test a blood sample was obtained from the earlobe at the third to fifth minute of recovery to determine Lab by means of a portable lactate analyzer (Lactate pro LT 1710, Arkray, Japan). The following parameters were thus obtained: • The average values of HR, VO2, VCO2, VE, and RER as measured in the last 2 minutes of exercise (when metabolic data have reached a sort of steady state, see Figure 1). • The Lab at the third to fifth minutes of recovery. All shuttle tests were performed within 2 weeks of the incremental test; when more shuttle tests were performed on the same day, they were separated by at least an hour of rest. The effective exercise intensity during each running bout (E′bout) was calculated on the basis of (1) the net VO2 measured between the 4th and 6th minute of exercise assuming that, in this condition, almost all the energy is derived from oxidative sources, either to sustain the energy needs during the bout or to replenish the phosphocreatine stores depleted during the exercise, and (2) net Lab. In turn, VO2net was calculated by subtracting resting metabolic rate (measured in the same subjects while standing for 5 minutes before the shuttle test) to the measured VO2 at steady state, and Labnet (the net Lab accumulated at the end of the test) was calculated assuming that Lab at rest equals 1 mM. The energy derived from oxidative sources, per unit of time and per kilogram of body mass (E′O2, mL · min–1 · kg–1), can be calculated as E′O2 = VO2net × ttot/te, where ttot/te is the ratio between the overall duration of each subunit of an exercise cycle (ttot: a bout plus its recovery period) and the duration of each exercise bout (te). This equation takes into account that te (as well as the work-to-rest ratio) changes with the shuttle distance.

Figure 1 — Typical tracing of oxygen uptake (VO2) as a function of time (t) during a shuttle test over the 10-m distance with a change of direction of 180°. After each bout of exercise VO2 increases sharply to further decrease in the following 30 seconds of recovery. The values of VO2 reported in this study (and the values of the other metabolic parameters) were obtained by averaging the data obtained in the last 2 minutes of exercise (when a sort of steady state is reached).

The energy derived from anaerobic lactic sources, per unit of time and per kilogram of body mass (E′La, mL · min–1 · kg–1), can be calculated by dividing Labnet by the number of exercise bouts (10) and by assuming an energy equivalent of 3.3 mL · kg–1 · mM–1, as follows18: E′La = (Labnet/10) × 3.3. Hence, the effective exercise intensity during each running bout (E′tot bout, mL · min–1 · kg–1) can be calculated as E′bout = E′O2 + E′La, and the net energy expenditure during the bout (Ebout net, mL/kg) can be calculated as Ebout = E′bout × te, where te is the duration (min) of each exercise bout. Finally, the effective net energy cost of running during the intermittent exercise (Cnet) can be calculated from the ratio of Ebout to the average distance (d) covered during the bout19: Cnet = Ebout/d. Cnet was then expressed in J · m–1 · kg–1 using an energy equivalent of 20.9 J/mL O2. This set of calculations was recently proposed by Zadro et al7 to assess the energy expenditure during supramaximal shuttle runs over a 20-m distance. The reader is referred to that article for a detailed discussion of the energy balance in this type of intermittent exercise. Suffice here to say that with this protocol (30 s of recovery between bouts) a complete replenishment of the anaerobic alactic energy stores occurs between bouts (during recovery), so to assess metabolic energy expenditure, it is necessary to take into consideration the aerobic and anaerobic lactic energy sources only.20

Statistical Analysis Data are presented as mean ± SD. A Shapiro-Wilk test was performed for the evaluation of normality (assumption) for statistical distribution. The effect of distance on the physiological variables investigated in this study was assessed by a 1-way ANOVA for repeated measures, and the level of significance was set at P < .05. When a significant F value was found, a Bonferroni post hoc test was applied. The same procedure was used to assess the effect of the change of direction on the investigated physiological variables.

1036  Zamparo et al

Statistical analysis was performed using SPSS for Windows (SPSS Statistics 17.0).

Downloaded by University of Exeter on 09/25/16, Volume 9, Article Number 6

Results In Table 1, the data collected during the incremental test are reported. The average VO2max was about 54 mL · min–1 · kg–1, and the ventilatory threshold occurred at 84% of VO2max (91% of HRmax); the corresponding average speed (vthr) was 4.00 m/s. The intensity of the intermittent exercise (the intermittent speed, vi = 120% vthr) was then larger than the speed attained at VO2max (vi = 4.80 m/s and vmax = 4.51 m/s). A typical tracing of VO2 as a function of time during a shuttle run is reported in Figure 1 (10 m, 180°). After each bout of exercise VO2 increases sharply to further decrease in the following 30 seconds of recovery; in the last 2 to 3 minutes of exercise a sort of steady state is reached (in all metabolic parameters). In Table 3, the data collected during the shuttle runs over the 10-m distance and with different changes of direction (0°, 45°, 90°,

and 180°) are reported. No major differences among conditions were detected for v, VO2, VE, HR, and Ebout, whereas RER, Lab, and Cnet were found to be significantly larger when the change of direction was performed at 180° than at 90° (see also Table 4 for ANOVA results). The values of Cnet reported in Table 3 are 5 times larger than those of running at constant speed on flat terrain (about 4 J · m–1 · kg–1, see Table 1) and are similar among conditions (range 20.5–22.14 J · m–1 · kg–1). These data indicate that for a given running distance there are no major differences in energy cost when the shuttle runs are performed with different changes of direction (the effect size is rather small: .33; see Table 4). Differences in the energy required to perform the change of direction are probably too small to lead to substantial changes in the physiological parameters except for the change of direction of 180°, which seems to be the more demanding one. In Table 5 the data collected during the shuttle runs with a change of direction of 180° over 3 different distances (5, 10, and 25 m) are reported. All parameters changed significantly among conditions (see Table 4 for ANOVA results). The players were not

Table 3  Physiological Data Collected During Intermittent Exercises (Shuttle Runs) Over a 10-m Distance With Different Changes of Direction Change of Direction 10 m



45°

90°

180°

4.68 ± 0.24*

4.61 ± 0.24*

4.93 ± 0.20

4.51 ± 0.20*

2.80 ± 0.18

2.78 ± 0.21

2.75 ± 0.21

2.83 ± 0.27

33.6 ± 1.94

33.3 ± 2.04

32.9 ± 1.74

33.9 ± 0.6

Heart rate (beats/min)

158 ± 6.7

163 ± 5.5

160 ± 8.9

163 ± 6. 9

Minute ventilation (L/min)

85.5 ± 7.1

88.1 ± 7.4

81.8 ± 0.1

89.8 ± 8.8

Respiratory-exchange ratio

0.99 ± 0.10*

0.91 ± 0.05†

0.87 ± 0.06

1.04 ± 0.09*

Net blood lactate concentration (mM)

3.4 ± 1.1

3.6 ± 1.1

2.8 ± 0.8

5.2 ± 1.9 *

Net energy expenditure during a shuttle run (mL/kg)

19.2 ± 1.1

19.0 ± 1.1

18.7 ± 0.9

19.5 ± 0.3

Net energy cost of shuttle running (J · m–1 · kg–1)

21.2 ± 1.0

21.2 ± 1.3

20.5 ± 1.0

22.1 ± 0.9*

Average speed (m/s) Oxygen uptake (L/min) Oxygen uptake (mL ·

min–1

·

kg–1)

*Statistical difference with 90° (P < .05). †Statistical difference with 180° (P < .05).

Table 4  Results of the Statistical Analysis (1-Way ANOVA) Change of Direction

Shuttle Distance

F3,24

P

η2

F2,16

P

η2

Average speed (m/s)

10.906

Energetics of shuttle runs: the effects of distance and change of direction.

Shuttle runs can be used to study the physiological responses in sports (such as basketball) characterized by sprints (accelerations/ decelerations) a...
173KB Sizes 1 Downloads 3 Views