5.5. Proyecto educativo
5.5.4. Evaluación del proyecto educativo
A.Ferrauti and K.Weber
Institute of Sports Games, German Sport University Cologne, Cologne, Germany
1 Introduction
Controversy still exists concerning the potential ergogenic benefit of caffeine. A decreased glycogen depletion due to an increased lipolysis and lipid oxidation, an enhancement of neuromuscular function and an optimisation of central nervous system function has been discussed (Powers and Dodd, 1985; Jacobson and Kulling, 1989). In some cases increases in aerobic (Ivy et al., 1979) and anaerobic endurance (Anselme et al., 1992) were found after caffeine ingestion.
Nevertheless, several studies have failed to exhibit a beneficial effect (Butts and Crowell, 1985; Powers et al., 1983).
The ergogenic value of caffeine has not yet been investigated in ball games. In addition to metabolic effects, positive responses can be expected to occur, due to the high mental and neuromuscular demands in this type of sports. From a practical viewpoint, commercially available beverages are of special interest due to the current flood of caffeine-containing “designer-energy drinks” on the European market. Thus, the purpose of this investigation was to determine the effects of caffeine in amounts typically used in soft drinks, on metabolic responses, playing success, hitting accuracy, running speed and perception during a long-lasting and interrupted tennis competition.
2 Methods 2.1 Subjects
Sixteen tournament tennis players (division II in German Tennis Federation), eight male (mean±SD: age 25.4±1.9 years, height 184±5 cm, mass 81.1±7.3 kg) and eight female (age 20.4 ±2.8 years, height 170 ±4 cm, mass 65.0 ±4.6 kg) participated in the study. Subjects were not regular consumers of caffeine (<150 mg.day-1), were non-smokers and were not taking any medication during the
experimental period. The players were familiar with all test procedures.
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Performance in tennis after caffeine ingestion 61 2.2 Procedure
Each player was tested on two occasions separated by at least three days. Subjects were asked to refrain from exercise during the last three days before trials and to abstain from caffeine consumption and also to maintain the same prescribed diet 24 hours prior to each trial. During the test days subjects received a standardized breakfast (08:00 h) and a carbohydrate-rich lunch (12:30 h) in order to simulate typical pre-match conditions. Between 15:00 h and 19:30 h players participated in a singles competition of 240 min on clay courts, according to the rules of the International Tennis Federation. The competition was interrupted after 150 min by a 30 min break. Immediately after the end, players were asked to perform a ball- machine test (BMT) to assess hitting accuracy and a tennis-sprint test (TST). Perception ratings were recorded continuously during match-play.
Players ingested an orange flavoured placebo (PLA) with no caloric value (provided by Sandoz Nutrition Ltd, Bern, Switzerland) or PLA supplemented with 130 mg.l-1 caffeine (CAF). In CAF, the drink treatment matched the average
caffeine content of coke drinks. Fifteen minutes after starting to play, and every following 15 min (at court changeover) the players consumed 150 ml (men) or 100 ml (women) of the assigned fluid. During the break 400 ml were ingested
containing 52 mg caffeine in CAF. Additionally, the subjects were allowed to drink water ad libitum. The total amount of standard ingestion in men (women) was 2.8 l (2.0 l) of fluid, supplemented with 364 mg (260 mg) caffeine in CAF. The
treatment drinks were assigned double-blind in a counter-balanced pattern. 2.3 Measurements and analyses
Metabolic parameters: Capillary blood samples were analysed for glucose (0, 15, 30, 90, 150, 180, 195, 210, 270 min; Cobas-Bio-System, Hoffmann-La Roche, Basel, Switzerland) and lactate (0, 75, 150, 270 min; Eppendorf-Analyser 5060, Hamburg, Germany). Venous blood samples were taken from an antecubital vein at rest and immediately post-exercise. Serum concentrations of free fatty acids (FFA) and glycerol (Cobas-Bio-System) as well as haemoglobin and haematocrit (Sysmex Dualdilutor DD100, Digitana AG, Germany) were determined. Urine concentrations of adrenaline and noradrenaline were analysed using HPLC (Chromsystems, München, Germany) and related to creatinine (Great) to eliminate differences in renal water handling. Caffeine determination was carried out with HPLC by direct urine injection. Heart rate was monitored in 15 s intervals (Polar Sport-Tester, Kempele, Finland).
Hitting accuracy: A standardized ball-machine test (BMT) was applied (Weber, 1987). Two players were instructed to return a randomized sequence of four successive forehand (FH) or backhand (BH) ground-strokes (20 balls.min-1)
alternating cross and long-line into a target area at the opponents’ base-line. Percentage of valid strokes during a 10 min test-period was recorded. Before each skill session, a 60 s warm-up period was permitted.
Running speed: Specific sprint performance was determined by a tennis-sprint test (TST) with electronic time measurement (Ferrauti, 1993). Subjects performed six base- line sprints (from central position to FH(BH)-corner and back to BH(FH)-corner), each
62 Ferrauti and Weber
a total of 15 m length and interrupted by a 30 s break. A newly developed stroke simulator transferred stop signals and guaranteed a tennis-specific movement pattern.
Perception: A newly developed perception scale was applied to assess “energetic drive” (ED-scale). This scale consists of numbers ranging from 1 to 10 with description words printed beside them (range from “very low” to “very high energetic drive”). The intention was not to investigate acute central or local exertion (Borg, 1982), but rather to evaluate superior items. In the present study the rating of energetic drive appeared to be advantageous, since other perception scales described in the literature are primarily reflecting the cardiopulmonary aspects of exertion (Borg 1982). Perception was estimated simultaneous to measurements of glucose. Sufficient time for recovery from the preceeding rallies was ensured.
2.4 Statistics
Data are presented as means and standard deviations. A multifactorial analysis of variance (ANOVA) with repeated measurements was used to determine statistical differences. In case of significance, simple effects were verified by means of Newman-Keuls test. Significance level was set at P<_0.05.
3 Results
Glucose in capillary blood decreased in both treatments from beginning to end by 15 % (Figure 1). During the first 15 min a distinct decrease in glucose immediately followed by an increase, was noted. This recurred after the break only in PLA. At this time point, glucose was maintained in CAF at a significant higher level (Figure 1). No considerable differences in glucose were found between men and women. Serum FFA and glycerol changes during competition were nearly identical in PLA and CAF but tended to a higher increase in women in case of caffeine ingestion (Figure 2). Plasma volume increased in both treatments equally by 5–6 % (Van Beaumont, 1972).
Urine concentrations of adrenaline and noradrenaline were significantly elevated after the competition. No differences as to gender and treatment were found for noradrenaline (Figure 2). In contrast, increases of adrenaline were significantly higher in men than in women and in women higher in CAF than in PLA. Urine post-exercise caffeine concentration increased only in CAF (6.6±1.1
g.ml-1), ranged from 5.5 to 9.3 g.ml-1 and did not differ between men and
women. In all subjects caffeine concentration remained below the doping limit (12 g.ml-1) of the International Olympic Committee.
Performance in tennis after caffeine ingestion 63
Figure 1. Capillary blood glucose during a tennis competition under caffeine feeding.
Figure 2. Absolute changes (D) of serum free fatty acids (FFA) and glycerol as well as urinary adrenaline and noradrenaline concentrations during a tennis competition under placebo (PLA) and caffeine feeding (CAF) in men and women.
64 Ferrauti and Weber
Table 1. Heart rate (HF), blood lactate and playing success (won games) during a tennis competition and post-exercise hitting accuracy (BMT) and sprint performance (TST) under placebo (PLA) and caffeine (CAF) feeding in men and women (n=8)
Figure 3. Perceived energetic drive (ED-scale) during tennis competition under caffeine feeding in women.
Performance in tennis after caffeine ingestion 65 Blood lactate and heart rate did not differ between CAF and PLA but were higher in men than in women (Table 1). These findings were significant only for lactate (P<_0.05). Significant differences in TST and BMT depending on the fluid supplementation did not occur. The only statistically significant effect on performance was gender-specific and occurred in respect to the measured game success. Women in CAF played more successfully (won games) than in PLA (P<_0.01) and achieved a better hitting accuracy in BMT (Table 1). These data correspond to the results of our perception ratings. In women, there was a significantly higher “energetic drive” during the last hour of the CAF trial, while no such effects were found in men (Figure 3).
4 Discussion
Blood glucose levels in CAF and PLA tended to be almost identical (Figure 1). Obviously, there was no evidence that the caffeine beverage provided had any glucose sparing effect during continuous match-play in tennis. Blood glucose data corresponded with the fact that there was no influence on lipolysis in CAF. Although both FFA and glycerol concentrations tended to be higher under caffeine treatment, these values did not differ significantly from those in PLA (Figure 2). This would contradict the observation of increased FFA levels and fat oxidation following caffeine ingestion (Ivy et al., 1979). The carbohydrate-rich pre-exercise meal was provided in the present study to simulate a typical match condition. According to other researchers, caffeine does not have significant metabolic effects after a high carbohydrate diet (Weir et al., 1987). Moreover, metabolic benefits of caffeine were usually measured after providing a higher caffeine dosage during the pre-exercise phase (Costill et al., 1978). In the present study a lower amount and a continuous form of administration was applied. It is concluded, that under these conditions no clear beneficial effects of caffeine on energy metabolism can be expected.
Caffeine ingestion resulted in a higher rise of urine adrenaline concentrations (Figure 2). Thus, we assume an augmented overall sympathetic activity in CAF. As expected, the effects of caffeine on adrenaline were independent of noradrenaline changes due to an immediate central nervous system stimulation of the adrenal medulla (Graham and Spriet, 1991). In contrast to the PLA trial there was no significant decline of blood glucose following the break of competition in CAF, but rather a more harmonious curve (Figure 1). It cannot be ruled out that the
increased sympathetic activity, especially after previous rest, guarantees a quicker glycogenolytic response to the sudden occurrence of glucose oxidation under beginning physical demands. This observation hints at an ergogenic effect of caffeine as a pre- or inter-exercise drink. Thus, beverages containing caffeine may improve the metabolic transition from rest to physical activity in tennis.
In men, the players’ success (games won) and hitting accuracy (BMT) did not benefit from caffeine. Nevertheless, a higher performance was shown by the women, who won significantly more games in CAF (Table 1). Furthermore, only women registered an elevated “energetic drive” during the last hour of competition (Figure 3). The underlying causes for these results are unknown. Gender-specific
66 Ferrauti and Weber
reactions to caffeine have not yet been proved (Butts and Crowell, 1985). A doseage effect can be ruled out, since in relation to body mass the women were given less caffeine (40 vs 4.5 mg.kg-1). Thus, the lower intensity in the women’s
matches (Table 1) and their smaller usual caffeine consumption (70 vs 110 mg.day- 1) offer the only grounds for explanation. It has been shown that caffeine effects are
increased in caffeine-naive subjects (Dodd et al., 1991). In fact, the women tended to reveal a more sensitive reaction in catecholamines after caffeine ingestion (Figure 3). In view of the lower physical demands, this might have stimulating mental effects. Caffeine had been shown to have a positive influence on alertness, wakefulness and mental activity at rest (Goldstein et al., 1965). As the exercise intensity was higher in men, these effects may be masked by the elevated exercise induced sympathetic responses (Perkins and Williams, 1975).
5 Conclusions
Results of the present study indicate that caffeine had no definite ergogenic effects on energy metabolism during long-lasting tennis competitions. Nevertheless, there were some indications that caffeine accelerates the regulation of blood glucose at the beginning of match-play and has specific ergogenic effects on performance and perception in women’s tennis. The intake of caffeine containing beverages can be suggested only for those players who 1) frequently complain about hypoglycaemic symptoms at the beginning of match-play and/or 2) usually achieve an insufficient level of physical and mental activity during the match.
The study was supported by the German Federal Institute for Sport Science, Cologne (BISP: VF 0407/01/52/95).
6 References
Anselme, F., Collomp, K., Mercier, B., Ahmaidi, S. and Prefaut, C.H. (1992) Caffeine increases maximal anaerobic power and blood lactate concentration. European Journal
of Applied Physiology, 65, 188–191.
Beaumont Van, W. (1972) Evaluation of hemoconcentration from hematocrit measurements. Journal of Applied Physiology, 32, 712–713.
Borg, G.A.V. (1982) Psychophysical bases of percieved exertion. Medicine and Science in
Sports and Exercise, 14, 377–381.
Butts, N.K. and Crowell, D. (1985) Effect of caffeine ingestion on cardiorespiratory endurance in men and women. Research Quarterly, 56, 301–305.
Costill, D.L., Dalsky, G.P. and Fink, W.J. (1978) Effects of caffeine ingestion on
metabolism and exercise performance. Medicine and Science in Sports and Exercise, 10, 155–158.
Dodd, S.L., Brooks, E., Powers, S.K. and Tulley, R. (1991) The effects of caffeine on graded exercise performance in caffeine naive versus habituated subjects. European
Journal of Applied Physiology, 62, 424–429.
Ferrauti, A. (1993) Relevance, diagnosis and training of running speed in high performance tennis , in Proceedings of 2nd Maccabiah-Wingate International
Congress in Sport Science and Coaching (eds G.Tenenbaum, T.Raz-Liebermann),
Performance in tennis after caffeine ingestion 67
Goldstein, A., Kaizer, S. and Warren, R. (1965) Psychotropic effects of caffeine in man. II. Alertness, psychomotor coordination and mood. Journal of Pharmacological
Experimental Therapeutics, 150, 146–151.
Graham, T.E. and Spriet, L.L. (1991) Performance and metabolic response to a high caffeine dose during prolonged exercise. Journal of Applied Physiology, 71, 2292–2298. Ivy, J.L., Costill, D.L., Fink, W.J. and Lower R.W. (1979) Influence of caffeine and
carbohydrate feedings on endurance performance. Medicine and Science in Sports and
Exercise, 11, 6–11.
Jacobson, B.H. and Kulling F.A. (1989) Health and ergogenic effects of caffeine. British
Journal of Sports Medicine, 23, 34–40.
Perkins, R. and Williams, M.H. (1975) Effect of caffeine upon maximal muscular endurance of females. Medicine and Science in Sports and Exercise, 7, 221–224. Powers, S.K., Byrd, R.J., Tulley, R. and Callender, T. (1983) Effects of caffeine ingestion
on metabolism and performance during graded exercise. European Journal of Applied
Physiology, 50, 301–307.
Powers, S.K. and Dodd S. (1985) Caffeine and endurance performance. Sports Medicine, 2, 165–174.
Weber, K. (1987) Der Tennissport aus internistisch-sportmedizinischer Sicht. Richarz, St. Augustin.
Weir, J., Noakes, T.D., Myburgh, K. and Adams, B. (1987) A high carbohydrate diet negates the metabolic effects of caffeine during exercise. Medicine and Science in
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