To Determine the Effect of an Exercise Regime on Heart Rate and Recovery Time
Introduction
The events of the cardiac cycle are initiated and controlled by electrical signals generated by two nodes in the heart (Boyle and Senior, 2008). Nodes are specialised tissues strategically placed in the heart that act as nervous and muscle tissue. When nodal tissue contracts, it generates nerve impulses that travel throughout the heart wall (About.com, n.d.).
Figure 1 – Cardiac Conduction
Yellow Arrows/Aspects = journey of signals
Area of Bundle of His/Purkinje Fibres
Ventricular Septum
Aorta – to the body
Pulmonary Artery – to the lungs

The location of the cardiac nodes is shown in figure 1. A single heartbeat begins with an electrical signal generated by the sino-atrial node, on the wall of the right atrium. This node is often referred to as the ‘pacemaker’ of the heart (it regulates the heartbeat). This signal spreads over the walls of both atria, causing them to contract and fill the ventricles.
Once the ventricle walls have filled, the atrio-ventricular node picks up the signal and directs it down the ventricular septum and onto the bundle of His. From here, the signal spreads throughout the Purkinje fibres in the ventricle walls causing them to contract, pushing the blood out of the pulmonary artery and aorta.

(Drugline.ord, n.d.)

Heart rate is controlled by the two branches of the autonomic nervous system - the sympathetic and parasympathetic. The sympathetic nerves increase your heart rate while you exercise. The sino-atrial node receives information from cardiovascular centre in the brain (medulla) which receives information from receptors in the aorta and carotid arteries about high levels of carbon dioxide in the blood. The parasympathetic nerves slow the heart rate when you are finished - it receives information from receptors via the vagus nerve. These branches are aided by hormones. The sympathetic secretes adrenaline (the arteries contract and blood is forced through at a faster rate) and the parasympathetic system secretes acetylcholine (slows the heart rate by increasing potassium and decreasing calcium and sodium movement)(Livestrong, 2011b).
Several factors other than exercise affect heart rate. Adrenaline secretion raises the heart rate to prepare the body for fight/flight. Therefore the heart rate increases to supply the body with extra oxygen and to remove excess carbon dioxide (Boyle and Senior, 2008). Caffeine consumption (stimulant), weight (the heart has more body to supply) and smoking (nicotine restricts blood vessels and carbon monoxide increases) mean heart rate increases as it struggles to deliver oxygen/remove CO2 (Livestrong.com, 2011a).
Recovery time is how quickly your heart rate goes down to its resting rate after cardiovascular exercise (Livestrong, 2010). When the body is recovering from exercise, receptors detect the reduced demand for oxygen and blood circulation and the heart rate slows accordingly.
There is extensive research evaluating the benefits of exercise for cardiovascular health. Kohl et al (1992) suggested that risk of sudden cardiac death was strongly associated with those who rarely exercised in comparison to those who do so habitually. They also state that regular exercise (at least 30 minutes, 3 times per week) reduces the chances of mortality associated with poor cardiac health. Brooks et al (2005) quoted that ‘heart rate does decrease over time with regular exercise training’. They suggested that with aerobic activity, the body makes physiological changes which make it easier for your heart to pump blood and oxygen around the body.
This investigation will explore the effect of cardiovascular exercise on resting heart rate and recovery time and the life implications of such a variable.

Hypothesis
If regular exercise is undertaken then resting heart rate and recovery time will decrease.
Apparatus
* 6 volunteers * 3 females, 3 males * Aged between 18 and 23 * 2 unfit, 2 moderately fit and 2 fit * Trainers * Running clothes * Health questionnaire * Stopwatch * Paper * Pen * Calculator
Method
1. Preceding the task, the weather forecast was checked and meeting times agreed. Health and safety precautions were discussed. All volunteers checked for safe exercise equipment. 2. All volunteers completed a health questionnaire and signed a contract of involvement. 3. A jogging route was planned and the warm up took place. 4. The resting heart rate (dependent variable) of volunteers was taken by counting the beats of the heart for 10 seconds and multiplying it by 6. Volunteers placed 2 fingers on the neck just below the jaw line and counted the beats felt in the time stated. 5. The resting heart rates were recorded. 6. All volunteers jogged for 30 minutes as cardiovascular exercise (independent variable). 7. Straight after exercise, the heart rate was taken using the same method as stated above. 8. Simultaneously, the stopwatch was set for 30 seconds. 9. After 30 seconds, the heart rate was taken again and recorded. 10. Steps 9-10 were repeated until the heart rates of all volunteers had returned to their personal resting heart rate. A cool down took place. 11. Steps 1 and 4-10 were repeated three times per week for two weeks, with at least one day of rest in between the sessions. The same route was used for each session.
Results
| Volunteer 1 - unfit | Time Post-exercise/Minutes | RHR = Resting Heart Rate
SA = Straight After (heart rate, exercise)
Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 78 | 78 | 78 | 78 | 72 | 72 | SA | 162 | 150 | 168 | 162 | 162 | 156 | 30 | 144 | 144 | 156 | 156 | 144 | 150 | 1 | 138 | 138 | 144 | 144 | 138 | 144 | 1.5 | 132 | 126 | 138 | 138 | 132 | 138 | 2 | 126 | 120 | 132 | 132 | 126 | 132 | 2.5 | 120 | 114 | 126 | 126 | 120 | 126 | 3 | 120 | 114 | 108 | 120 | 114 | 120 | 3.5 | 114 | 108 | 108 | 120 | 108 | 120 | 4 | 114 | 108 | 102 | 114 | 108 | 114 | 4.5 | 114 | 102 | 102 | 114 | 102 | 114 | 5 | 114 | 102 | 96 | 108 | 102 | 108 | 5.5 | 102 | 102 | 96 | 108 | 96 | 102 | 6 | 108 | 96 | 90 | 102 | 90 | 96 | 6.5 | 102 | 96 | 90 | 96 | 84 | 90 | 7 | 96 | 96 | 84 | 96 | 78 | 84 | 7.5 | 90 | 90 | 84 | 90 | 78 | 78 | 8 | 84 | 84 | 84 | 84 | 72 | 72 | 8.5 | 78 | 78 | 78 | 78 | | | | Volunteer 2 - unfit | Time Post-exercise/Minutes | Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 78 | 78 | 66 | 78 | 78 | 78 | SA | 174 | 174 | 174 | 174 | 174 | 174 | 30 | 168 | 168 | 168 | 168 | 168 | 168 | 1 | 168 | 168 | 162 | 168 | 168 | 168 | 1.5 | 162 | 162 | 156 | 162 | 162 | 162 | 2 | 156 | 156 | 150 | 162 | 156 | 156 | 2.5 | 150 | 150 | 150 | 150 | 150 | 150 | 3 | 144 | 144 | 144 | 144 | 144 | 144 | 3.5 | 138 | 138 | 138 | 138 | 138 | 138 | 4 | 126 | 120 | 138 | 126 | 126 | 126 | 4.5 | 120 | 114 | 126 | 120 | 120 | 120 | 5 | 114 | 108 | 120 | 114 | 114 | 114 | 5.5 | 102 | 102 | 102 | 102 | 102 | 102 | 6 | 96 | 96 | 96 | 96 | 96 | 96 | 6.5 | 90 | 96 | 90 | 90 | 96 | 90 | 7 | 84 | 84 | 84 | 84 | 84 | 90 | 7.5 | 78 | 78 | 78 | 78 | 78 | 78 |

| Volunteer 3 – moderately fit | Time Post-exercise/Minutes | Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 72 | 72 | 72 | 72 | 72 | 66 | SA | 144 | 132 | 144 | 144 | 132 | 132 | 30 | 132 | 126 | 126 | 126 | 126 | 126 | 1 | 126 | 120 | 120 | 120 | 120 | 120 | 1.5 | 120 | 114 | 114 | 114 | 114 | 114 | 2 | 114 | 108 | 108 | 108 | 108 | 108 | 2.5 | 108 | 108 | 108 | 102 | 102 | 102 | 3 | 102 | 96 | 102 | 96 | 96 | 102 | 3.5 | 102 | 96 | 96 | 90 | 96 | 96 | 4 | 96 | 96 | 84 | 90 | 90 | 96 | 4.5 | 96 | 84 | 84 | 84 | 84 | 90 | 5 | 84 | 84 | 84 | 78 | 84 | 84 | 5.5 | 78 | 78 | 78 | 72 | 78 | 66 | 6 | 72 | 72 | 72 | | 72 | | | Volunteer 4 – moderately fit | Time Post-exercise/Minutes | Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 72 | 72 | 72 | 72 | 72 | 72 | SA | 144 | 144 | 144 | 144 | 144 | 144 | 30 | 132 | 132 | 132 | 132 | 132 | 132 | 1 | 120 | 126 | 126 | 126 | 126 | 126 | 1.5 | 120 | 120 | 120 | 120 | 120 | 114 | 2 | 114 | 114 | 114 | 114 | 114 | 114 | 2.5 | 108 | 108 | 108 | 108 | 108 | 108 | 3 | 102 | 102 | 108 | 102 | 102 | 102 | 3.5 | 102 | 102 | 102 | 102 | 102 | 102 | 4 | 96 | 96 | 102 | 96 | 96 | 96 | 4.5 | 96 | 96 | 96 | 96 | 96 | 96 | 5 | 78 | 84 | 84 | 84 | 84 | 84 | 5.5 | 78 | 78 | 78 | 78 | 78 | 78 | 6 | 72 | 72 | 72 | 72 | 72 | 72 |

| Volunteer 5 - fit | Time Post-exercise/Minutes | Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 66 | 66 | 66 | 66 | 66 | 66 | SA | 156 | 156 | 156 | 156 | 156 | 156 | 30 | 150 | 150 | 150 | 150 | 150 | 150 | 1 | 144 | 138 | 138 | 138 | 138 | 138 | 1.5 | 138 | 126 | 126 | 126 | 126 | 126 | 2 | 126 | 120 | 120 | 120 | 120 | 120 | 2.5 | 120 | 114 | 114 | 114 | 114 | 114 | 3 | 114 | 108 | 102 | 108 | 108 | 108 | 3.5 | 102 | 90 | 90 | 102 | 102 | 96 | 4 | 90 | 84 | 78 | 96 | 96 | 84 | 4.5 | 78 | 72 | 72 | 78 | 72 | 78 | 5 | 66 | 66 | 66 | 66 | 66 | 72 | 5.5 | | | | | | 66 |

| Volunteer 6 - fit | Time Post-exercise/Minutes | Session | | 1 | 2 | 3 | 4 | 5 | 6 | RHR | 66 | 66 | 66 | 66 | 66 | 66 | SA | 156 | 156 | 156 | 156 | 156 | 156 | 30 | 144 | 144 | 144 | 144 | 144 | 144 | 1 | 132 | 132 | 132 | 132 | 132 | 132 | 1.5 | 126 | 126 | 126 | 126 | 126 | 126 | 2 | 114 | 114 | 114 | 114 | 114 | 114 | 2.5 | 102 | 102 | 102 | 102 | 102 | 102 | 3 | 90 | 90 | 90 | 90 | 90 | 90 | 3.5 | 78 | 78 | 78 | 78 | 78 | 78 | 4 | 72 | 72 | 72 | 72 | 72 | 72 | 4.5 | 66 | 66 | 66 | 66 | 66 | 66 |

Observations/Analysis of Results
The following conclusions can be formed from the results. The resting heart rates of the five volunteers were largely unaltered with the exception of volunteer one whereby the resting heart rate reduced by one beat per minute by the fifth session, suggesting a small increase in cardiac fitness (previously unfit). This is also demonstrated by the reduction in recovery time by 30 seconds by the fifth session (seen in appendix 1 graph 1). Similarly, volunteer three experienced a reduction in resting heart rate by one beat per minute by the sixth session. This volunteer also experienced a reduced recovery time by 30 seconds in this session (seen in appendix 1 graph 3). This volunteer usually took part in strength focused exercise, so despite being moderately fit had scope for a slight improvement in cardiac fitness. The results of volunteers five and six show no change throughout the process suggesting that their cardiac fitness was equivalent or more developed than the exercise they were subject to in this investigation (seen in appendix 1 graphs 5 and 6). The same results can be deduced from the graphs in appendix 2. The similar shapes and gradients between these graphs demonstrate the lack of improvement in cardiac fitness across the board.
Discussion
These results can be applied and discussed extensively. Despite controlling conditions as far as possible, there are reasons why the results are slightly inconclusive. The length of the study was too short to notice a significant improvement in cardiac fitness (3/4 weeks may have been better). It was hard to control elements (e.g. weather) and speed. If the investigation was repeated an environment such as on a treadmill in the gym with speed/environmental control the results would be more valid. We could have used this setting as a control experiment (a variable-controlled example of the investigation). It was difficult to ensure all volunteers were measuring heart rate accurately. Heart rate monitors would have been more precise. The age range (shown in appendix 4, question 2) investigated could have been wider to further the depth of results. Individual differences/energy and sleep intake could also have negatively affected the validity of the results.
There are two anomalies seen in red in the results tables. In session three, volunteer two had had a very sedentary day and so when the resting heart rate was taken it was lower than usual. In session six, volunteer five took longer to return to their resting heart rate due to end of week fatigue.
Fitness has many implications on a person’s life and health. Living a sedentary lifestyle causes increased risk of chronic diseases and premature death. There are well-established links between physical exercise and reduced risk of cardiovascular disease (Rhodes et al, 2009). Conversely, research suggests that over-exercise can be detrimental to cardiac health. Elite athletes demonstrate an extreme level of cardiac fitness and can reduce their heart rates to as low as 40 beats per minute (Heart.com, 2009). However, they can also experience altered cardiac function, myocardial damage and long-term cardiac ill-health due to repetitive bouts of prolonged arduous exercise (Whyte et al, 2007). Such athletes can develop heart conditions such as pathological ventricular hypertrophy and idiopathic interstitial myocardial fibrosis. Ventricular hypertrophy is the enlargement of the ventricles as a result of continued strenuous exercise as the speed and strength (pressure) of the blood passing through causes stretching.

Myocardial fibrosis causes impairment of the heart’s muscle cells (myocytes). During fibrosis, myocytes are replaced by tissue that is unable to contract. Fibroblasts produce collagen to enable wound healing of small tears in the artery walls caused by repeated high blood pressure during exercise. This causes patchy scarring (normally in lines – see figure 2) making the heart inflexible and unable to pump blood as efficiently (Wisegeek, n.d.). These conditions are a pathological substrate for the development of arrhythmias and could result in death (Wilson et al, 2011).

Areas of collagen build up (myocardial fibrosis)
Journal of Clinical and Experimental Cardiology (2012)

Figure 2 – Myocardial Fibrosis

Over-exercise can cause other negative side-effects. The knees are susceptible to damage due to the weight bearing nature of many cardiovascular exercises. Ligament damage and the wearing of cartilage in joints are also common. If a person does not allow their body to repair itself post-exercise they may experience immune suppression (demonstrated with a low white blood cell count - especially phagocytes, B cells and helper T cells). This leaves them vulnerable to sore throats and flu-like illnesses (Boyle and Senior, 2008).
However, if little or no exercise is undertaken it makes a person more susceptible to heart disease (the reasons of which are now discussed). Exercise reduces blood pressure and this reduces the strain on the heart. It increases the quantity of high-density lipoproteins in the blood. These scavenge the low-density lipoproteins (bad cholesterols from the diet) which can contribute to the formation of atheromas in the heart (fatty deposits which narrow the coronary arteries and can lead to coronary heart disease)(Patient.co.uk, 2010). Exercise also improves circulation by preventing blood clots (thrombosis) that can lead to a heart attack or stroke (Netdoctor, 2013).
As cardiac fitness increases, recovery time reduces. This is because the heart muscle (myocardium) enlarges and the chamber size increases. Therefore, the stroke volume (volume of blood pumped with each beat) increases. With this, the heart does not have to beat as often to deliver the same amount of blood. Therefore the heart rate and recovery time of a fit person is lower than that of an unfit one (Boyle and Senior, 2008). Conclusion
My results show a weak correlation between cardiovascular exercise and resting heart rate and recovery time as displayed in the tables and graphs. This means that the hypothesis is neither supported nor disproved. The results are limited and no firm conclusions can be formed.

References
About.com (n.d.) Heart Nodes. [online] Available at: http://biology.about.com/od/anatomy/ss/heart-nodes.htm [Accessed: 21 Jan 2013].
Boyle, M. and Senior, K. (2008) Biology. 3rd ed. London: Collins.
Brooks, G. et al. (2005) Exercise Physiology. 4th ed. Boston: McGraw-Hill, p.0-22.
Drugline.org (n.d.) Electrical Conduction of the Heart. [image online] Available at: http://drugline.org/img/term/sa-node-13124_3.jpg [Accessed: 20 Jan 2013].
Heart.com (2009) Heart Rate Chart | Heart.com. [online] Available at: http://www.heart.com/heart-rate-chart.html [Accessed: 28 Jan 2013].
Journal of Clinical and Experimental Cardiology (2012) Myocardial Fibrosis. [image online] Available at: http://www.omicsonline.org/2155-9880/2155-9880-3-186.php?aid=5653 [Accessed: 19 Jan 2013].
Kohl, H. et al. (1992) Physical Activity, Physical Fitness, and Sudden Cardiac Death. Epidemologic Review, 14 (1), p.37-58. Available at: http://epirev.oxfordjournals.org/content/14/1/37.extract [Accessed: 19 Jan 2013].
Livestrong (2010) Post-Exercise Heart Rate Recovery. [online] Available at: http://www.livestrong.com/article/167218-post-exercise-heart-rate-recovery/ [Accessed: 9 Feb 2013].
Livestrong (2011a) Factors Affecting the Heart Rate. [online] Available at: http://www.livestrong.com/article/80175-factors-affecting-heart-rate/ [Accessed: 21 Jan 2013].
Livestrong (2011b) How Does the Nervous System Control the Heart Rate in Exercise?. [online] Available at: http://www.livestrong.com/article/422152-how-does-the-nervous-system-control-the-heart-rate-in-exercise/ [Accessed: 28 Jan 2013].
Netdoctor (2013) Exercise, heart disease and high blood pressure. [online] Available at: http://www.netdoctor.co.uk/heartdisease/exercise.htm [Accessed: 9 Feb 2013].
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Rhodes, R. et al. (2009) Characteristics of physical activity guidelines and their effect of adherence. British Journal of Sports Medicene, 39 p.355-75. [Accessed: 19 Jan 2013].
Whyte, G. et al. (2007) Post-mortem evidence of idiopathic left ventricular hypertrophy and idiopathic inerstitial myocardial fibrosis:is exercise the cause?. British Journal of Sports Medicene, 42 (4), p.304-05. Available at: bjsportmed.com/content/42/4/304.abstract [Accessed: 19 Jan 2013].
Wilson, M. et al. (2011) Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes. Journal of Applied Physiology, 110 (6), p.1622-26. Available at: jap.physiology.org/content/110/6/1622.full [Accessed: 19 Jan 2013].
Wisegeek (n.d.) What Is Myocardial Fibrosis? [online] Available at: http://www.wisegeek.com/what-is-myocardial-fibrosis.htm [Accessed: 28 Jan 2013].

Appendices
Appendix 1 – Graphs to Show Individual Results
Appendix 2 – Results from Session 1 in comparison with Session 6
Appendix 3 – Health Questionnaire Example
Appendix 4 – Health Questionnaire Results
Appendix 5 – Risk Assessment