Cardiovascular fitness refers to the ability of the heart and lungs to supply oxygen-rich blood to the working muscle tissues of the body and the ability of muscles to use oxygen to produce energy for movement. Cardiovascular fitness is developed by sustained physical activity and is a health-related measure of physical fitness. An individual’s ability to deliver oxygen to working muscles is affected by many physiological parameters, for instance, heart rate, stroke volume, cardiac output and maximal energy consumption (Xiang and Hester 2012). In this experiment, the influence of heart rate on cardiovascular fitness was investigated. Research has shown that individuals with high levels of cardiovascular fitness have lowered risks of developing heart-related diseases (Kostic et al. 2006).

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Resting heart rate, heart rate under strain and recovery time are several indicators that can be used to evaluate cardiovascular fitness. Resting heart rate is the normal heart of an individual measured in beats per minute or bpm. Heart rate under strain is the heart rate of an individual taken right after extraneous exercise or physical activity and is expected to be higher than their resting heart rate. Recovery time is the time it takes for heart rate after exercise to return to its resting heart rate. The faster an individual can recover after exercise, the better their cardiovascular fitness is (Gaesser and Rich 1984).
The purpose of this study was to investigate the effects of high and low exercise intensity on heart rate and recovery time. It can be predicted that as the intensity increases, there should be an increase in both the heart rate and recovery time. The alternate hypothesis of this experiment is that higher intensity will increase heart rate and recovery time. The null hypothesis, on the other hand, is that high intensity will have no effect on heart rate and recovery time.
MATERIALS AND METHODS
The lab group composed of Ayesha, Reena, Ryan and Pegah. The two subjects were Ryan and Ayesha, for low and high intensity, respectively. Ryan was a 19 year old male, physically active and an athlete. Ayesha was a 18 year old female and had not been involved in any form of regular physical activity in the past year.
The class was divided into four groups. Two people from each group were chosen to be the subjects for the study. The subject’s resting pulse rate was taken by placing two fingers on the carotid artery on the side of the neck, counting the number of beats in 30 seconds and multiplying by 2 to get beats per minute. Subject one (Ryan) then performed the step test for low intensity. The Step test was performed by stepping up and down on a gym bench, approximately 45cm in height for 3 minutes. Low intensity treatment required the subject to do 30 steps per minute for 3 minutes. Right after the test, the subject’s pulse rate was measure and recorded again. The recovery time was then recorded by allowing the subject to rest for 1 minute and taking his pulse rate at 30-second intervals. The above procedure was then repeated with subject 2, Ayesha, under high intensity conditions. The subject was required to do 60 steps per minute for 3 minutes.
Pulse rate and the recovery time were the dependent variables. They varied from subject to subject. Exercise intensity was the independent variable. Low intensity interpreted to 30 steps while high intensity was 60 steps per minute. Normal heart rate was the control. The duration of each treatment, room conditions and species of the subject were constant. The experiment was replicated the division of the class was into 4 groups. Therefore, four independent trials were performed with varying subjects. This way the experiment was replicated 4 times.
RESULTS
As demonstrated in table 1, the recorded pulse rates before and after the step test varied from subject to subject. Under low intensity treatment, the mean pulse rate before the step test was 60 bpm, while it increased to 69.5 bpm after the test, an increase of 9.5 bpm. Under high intensity treatment, the mean pulse rate before the step test was 66.5 bpm. After the step test, the pulse rate increased to 110 bpm, an increase of 43.5 bpm.
The standard error of the mean (SEM) for low intensity was 2.45 and 5.68, before and after the test respectively. SEM for high intensity before the test was 4.72 and 8.83 after the test. The higher SEM value after the test for higher intensity may be due to a larger increase in the mean as well.
The mean recovery time for low intensity was 60 seconds or 1 minute. The recovery time for the high intensity treatment was 92.5 seconds, approximately an increase of 33 seconds compared to 60 seconds for low intensity. The SEM value for the low intensity recovery time was 0. However, for high intensity the SEM value was relatively high, 12.99, demonstrating variance amongst the individual recovery times for high intensity treatment.
Figure 1 illustrates the mean pulse rate before and after each treatment. The error bars of pulse rates after low intensity and before high intensity are close but do not overlap. Figure 2 demonstrates mean recovery time versus the treatments. There is no error bar for low intensity due to the fact that the SEM value for low intensity was 0.
Table 1: Pulse rate before and after each treatment and recovery time
Treatment
Low Intensity
High Intensity
Subject
1
2
3
4
1
2
3
4
Mean
SEM
Mean
SEM
Pulse rate before the step test (bpm)
60
54
60
66
60
2.45
60
80
60
66
66.5
4.72
Pulse rate after the step test (bpm)
78
54
68
78
69.5
5.68
108
126
86
120
110
8.83
Recovery Time (s)
60
60
60
60
60
0
85
120
60
105
92.5
12.99
Figure 1: Mean pulse rate before and after each treatment
Figure 2: Mean Recovery Time associated with each treatment
DISCUSSION
The results comply with the expectations. The mean pulse rate before each treatment was very close, as can be seen in figure 1, the bars of before low and high intensity treatment are close in length. Secondly, the prediction that the mean pulse rate after high intensity should be much higher than the mean pulse rate after low intensity was accurate as well. It was also found that the mean recovery time for low intensity was much lower than the mean recovery time for high intensity.
The results make it clear that an increase in intensity results in an increase in heart rate. This confirms to the alternate hypothesis of the experiment that higher intensity will increase heart rate and recovery time. The results however do not agree with the null hypothesis that high intensity will have no effect on heart rate and recovery time. The hypothesis in this experiment was supported because the results were consistent with the alternate hypothesis and not with the null hypothesis. Therefore the alternate hypothesis was accepted, while the null hypothesis was rejected. Significant statistical significance was noted and there was no overlap in the SEM bars.
The evidence that accepts the hypothesis is that from Table 1 and figure 1, comparing the before and after mean pulse rate values for each treatment, it is clear that there is a much higher increase in high intensity than low intensity. The higher increase demonstrates that as the intensity increases, heart rate also increases accordingly. Another interesting observation is in the SEM values for after high intensity treatment pulse rate and high intensity recovery time, 8.83 and 12.99 present the possibility that the actual mean is actually larger or smaller than the one calculated because these values are high. This could be confirmed by carrying out more trials with high intensity treatment.
REFERENCES
Gaesser GA, Rich RG. 1984. Effects of high and low intensity exercise training on aerobic capacity and blood lipids. Med. Sci. Sports Exerc. 18(3):269-274.
Kostic R, Duraskovic R, Miletic D, Mikalacki M. 2006. Changes in the cardiovascular fitness and body composition of women under the influence of the aerobic dance. Facta. Univ. Phys. Educ. Sport. 4(1):59-71.
Xiang L, Hester RL. 2012. Cardiovascular responses to exercise. California: Morgan and Claypool Life Sciences.