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Exercise & Caffeine

Background

The effects of caffeine ingestion on physical performance, lactate production, heart rate and ratings of perceived exhaustion.

Introduction

Numerous review articles (Bell et al, 1998; Pasman et al, 1995; Spriet & Graham, 2000; Spriet et al, 1992; Vanakoski et al; 1998) have addressed caffeine ingestion and its influence on exercise capacity. Caffeine is a common substance in the diets of most athletes and it is now appearing in many new products, including energy drinks, sports gels, alcoholic beverages and diet aids. In recent years, research has suggested that caffeine can be used as a powerful ergogenic aid at levels that are considerably lower than the acceptable limit of the International Olympic committee and could be beneficial in training and in competition (Pasman et al, 1995 & Spriet et al, 1992). Caffeine is a legal, inexpensive and socially acceptable drug. In some competitive sports it is not banned and in others it is controlled or tolerated to a very high level. The association between caffeine ingestion and exercise capacity has been amply documented in previous studies (Pasman et al, 1995 & Spriet et al, 1992; Spriet & Graham, 2000; Bell et al; 1998). However, despite the firm association between caffeine ingestion and exercise capacity, further research is required to accurately establish the effects of caffeine ingestion on, not just performance but also, its underlying effects on lactate production, heart rate, and ratings of perceived exertion during exercise.

Several studies have examined the relationship between caffeine ingestion and endurance performance time (Pasman et al, 1995 & Spriet et al, 1992; Spriet & Graham, 2000; Bell et al; 1998). A number of researchers commonly measure endurance because, in this situation, power is kept constant and exercise time can be quantified. Most investigators have the participants ingest the caffeine dose relative to body weight, rest an hour and then exercise. This protocol has been selected because caffeine is rapidly absorbed and plasma concentrations approximate a maximum level in one hour. Pasman et al (1995) reported that a significant increase in endurance performance was found for all caffeine tests compared to placebo (endurance time 47 +/- 13, 58 +/- 11, 59 +/- 12 and 58 +/- 12 minutes for 0, 5, 9 and 13 mg.kg.-1 body weight, respectively). These results correlate with Spriet et al (1992) who found that caffeine ingestion prior to exercise coincided with a prolonged time to exhaustion. Further to this, a study conducted by Graham and Spriet (2000) examined subjects that ingested either a placebo or caffeine (9mg/kg) one hour before exercise and found that endurance times were increased after caffeine ingestion prior to running. Therefore, it is clearly evident that previous studies suggest that there is a positive relationship between caffeine and endurance performance and that this association highlights that caffeine is an ergogenic aid that stimulates endurance performance.

In contrast to the previous studies mentioned, results established through research by Bell and associates (1998) highlighted that caffeine did not have a significant effect on time to exhaustion during high intensity exercise. However, it should be noted that this aspect (high intensity endurance) of exercise has received less attention by researchers in this area as there is no evidence that glycogen is limiting in such activities. Therefore, there is further scope for research into this area. However, Bell et al (1998) did find that heart rate during exercise was significantly increased for the caffeine trials when compared to placebo. Further to this, subjective ratings of perceived exertion during exercise were significantly lower after the caffeine trial when compared to placebo and both treatments significantly increased lactate levels.

The collated research clearly suggests that caffeine ingestion has a positive effect on endurance for long term exercise; however the effect of caffeine ingestion has not yet been thoroughly explored in relation to its effect on endurance in short term intense exercise. Further, to this there appears to be a lack of quality research into the effects of caffeine ingestion on not just performance but also its underlying effects on lactate production, heart rate and ratings of perceived exertion during exercise.

Therefore, the purpose of the current study is two fold 1) to investigate the effect of caffeine ingestion on endurance in short term running performance (time trail to exhaustion) and 2) to examine the effects of caffeine ingestion on lactate production, heart rate and ratings of perceived exhaustion. It is hypothesized that caffeine ingestion will have a positive effect on improving endurance performance time and that caffeine ingestion will have a significant effect on lactate production, heart rate and subjective ratings of perceived exertion.

Methods

Experimental Design

Subjects were informed of the experimental procedure and consent for participation was received prior to commencement. The experiment was conducted using a double-blind protocol, over a two-week period. Week 1 consisted of a sub-maximal oxygen consumption test (VO2 sub-max test) to determine maximal oxygen uptake (VO2max), ingestion of an instant coffee (9mg of caffeine/kg) or placebo beverage, followed by a graded aerobic test to volitional exhaustion, and heart rate, blood lactate and rate of perceived exertion (RPE) assessment over specified, constant time periods. In Week 2, this procedure was repeated. Approval for this experiment had been obtained from the Queensland University of Technology Research Ethics Officer.

Subjects

Two voluntary female university students were selected as subjects for experimentation. Age and weight were established to be 20 yrs, 60 kg (Subject 1) and 26 yrs, 51 kg (Subject 2).

Experimental Procedure

In Week 1, on arrival, resting heart rate of each participant was recorded using heart rate monitors. Resting blood lactate was also recorded using a lactate analyzer and lactate strips. Identical treadmills containing timer, and graded incline and velocity adjustment features were the designated chief equipment used in the experiment. Subjects performed a VO2 sub-max test, running at a velocity of 8km/hr. Treadmills were set to 0% incline for a two minute warm up, followed by a further three minutes at this level. Heart rate was recorded at five minutes. This procedure continued, with incline increasing by 2% every three minutes and heart rate recorded at this time. Subjects were instructed to stop when a 6% incline was reached, and a final heart rate was taken. A two minute warm down at zero percent incline and 3km/hr was then completed. An instant coffee or placebo beverage (exact contents unknown to participant or experimenters) was ingested by each subject, and 40 min from this point was timed.

During the waiting period, 85% VO2 max and corresponding incline for each subject was accurately calculated using a computer program, which determined these figures using heart rate data obtained from the VO2 sub-max test and the subject’s age.

Prior to commencement of the aerobic test to volitional exhaustion, the heart rate and blood lactate of each subject was recorded. Both subjects undertook a two minute warm up (8km/hr velocity), each gradually building up to their calculated incline during this period. Both subjects covered their treadmill timers with a towel. Experimental procedure required that heart rate and RPE (measured using the Borg Scale) of each subject be recorded every three minutes, commencing at the five minute mark. Subject 2 began at an incline of 8%, increasing to 9% at 10 minutes, 10% at 12 minutes and 12% at 14 minutes. Subject 1 maintained her 9% incline throughout the testing period. After each subject reached their point of exhaustion, their time and final heart rate was recorded, and a two minute warm down at zero percent incline and 3km/hr was undertaken. A final blood lactate recording was taken five minutes post exhaustion time.

Experimentation in Week 2 strictly followed the exact procedure of the previous week, however new data collected from the VO2 sub-max test was not computer processed. Percent incline data determined in Week 1 was used.

Results

The 85% VO2 max test did not show a significant enhancement in performance after the ingestion of caffeine (see Table 1 for heart rate, lactate and rate of perceived exertion). Blood lactate increased post exercise in both trials for both subjects, with ratings of perceived exertion increasing as running time increased, however RPE is slightly higher in caffeine trials. Figure 1 shows the effects of caffeine on heart rate when running at 85% VO2 max. The heart rate of both subjects increased drastically in the first five minutes of running then continued to slowly increase to reach both subjects predicted VO2 max. Subject 1 showed a significant time effect when trialling the placebo (decaffeinated coffee) in contrast to the caffeine. Subject 2 displayed no significant difference in performance between the caffeine and placebo mixtures.

Discussion

This study investigated the effect on caffeine ingestion on endurance in short term running performance through conducting a time trial to exhaustion experiment, while also examining the effects of caffeine ingestion on lactate production, heart rate, and ratings of perceived exertion (RPE). This study revealed that the ingestion of caffeine (9mg/Kg) forty minutes before exercising to exhaustion at high intensity work load had no effect on time to exhaustion or running performance on two female Human Movement students ages 20 and 26.

The subjects either performed at a significantly higher level, increasing their time to exhaustion, or did not notably differ when had ingested the placebo trial. Both subjects displayed increased blood lactate levels, heart rate and RPE after exercise ceased in both trials; however, there was a higher RPE rating during the caffeine trials from both subjects. Both participants did not feel as comfortable after ingesting the caffeine, in comparison to the placebo; with Subject 2 producing a greater amount of perspiration during exercise with the caffeine.

Initially, this report hypothesized that caffeine would have a positive effect on improving endurance performance time and also positively effect lactate production, heart rate and RPE; however from our results, it is evident that these hypotheses are not supported. There are a number of external factors, which played a significant part in the subject’s performance on the day to produce these unexpected results. These consist of the condition of the athlete’s mental state at the time of trial, their eating patterns prior to performing, how their bodies were feeling (if they were sore, sick, had an injury) and how much sleep they had had in the past 24 hours. Subject 1 was complaining of stomach upset in the first trial as she had just ingested a large quantity of glucose prior to the experiment. This subject consumed the caffeine substance on this day and in review, her performance was inhibited by her stomachache. She learnt from this for the second trial and her performance displayed a significant improvement, even though she had taken the placebo.

In addition, both participants requested the data screen on the treadmills to be covered throughout the entire running period. This ensured the subjects could not see how much time had elapsed, what percentage incline they were running at, or what their heart rate was. This allowed the subjects to concentrate on the task and not be influenced by these factors in affecting their performance.

Moreover, the way the experiment was designed with the conduction being executed over two weeks, the subjects were exposed to what time they ran the first week, therefore affecting their mentality in how they were going to perform the following week. This enabled them to set a goal in which they could aim toward for the second trial; hence, improving on their performance. This could have been prevented if their total time ran during trial one was withheld from the participants until both trials were completed. This would have prevented the runners having an incentive to perform for a longer duration throughout trial two.

As previously mentioned, numerous researches have shown how beneficial the use of caffeine is on endurance during long-term exercise. However, the effect of this substance has not yet been thoroughly explored in relation to its effect on endurance in short-term high intensity exercise sessions. Further research needs to be undertaken in this field for our results to give a definitive comparison.

References

Bell, D., Jacobs, I & Zamecnik, J. (1998) Comparison of cafffeine and theophylline ingestion: exercise metabolism and endurance. Journal of applied physiology. 77(5), 427-433.

Pasman, WJ., Van Baak, MA., Jeujendrup AE., deHaan, A. (1995) The effects of different dosages of caffeine on endurance performance time. International Journal of Sports Medicine, 16(4), 225-30.

Spriet, L & Graham, T. (2000) Performance and metabolic responses to a high caffeine dose during prolonged exercise. Journal of Applied Physiology, 89(5), 1837-1844.

Spriet, L., Maclean, D., Dyck, D., hultman, E., Cederblad, G. & Graham, T. (1992) Caffeine Ingestion and muscle metabolism during prolonged exercise in humans. American Journal of Endocrinology and Metabolism. 262(6), 891-898.

Vanakoski, J., Kosunen, V., Meririnne, E., Seppala, T. (1998) Creatine and caffeine in anaerobic and aerobic exercise: effects on physical performance and pharmacokinetic considerations. International Journal Of Clinical Pharmacology and Therapeutics, 36(5), 258- 262.

Reproduced with the persmission from Veronika Larisova


 
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