The experiments aims were to run subjects to exhaustion on an increasing work rate in order to calculate changes in heart rate and VO2 consumption, in order to see if there was a correlation. Work rate started at 8km/h and increased by 2 km/h every 3 minutes. A strong positive correlation between increased work rate and a proportional increase in both heart rate and VO2 was found when assessing the results and formulating the graphs. All subject were male: age (19.43years ± 0.79), height (1.82 m ±0.10), weight (73.29kg ±15.11).
The aim was to determine oxygen uptake and carbon dioxide production at rest and during a bout of sub maximal exercise and what relationship it had with heart rate.
Heart rate itself is simply “the amount of work the heart must do to meet the increased demands of the body when engaging in activity” Wilmore and Costill 2004 page 224) measure it is usually done at the radial of carotid artery sites.
Heart rate in this case is an indicator of the relative stress placed on the cardio respiratory system during movement. “Heart rate increases during physical activity are controlled by the synoatorial node, in response to decreased parasympathetic neural stimulation, increased sympathetic neural stimulation- a phenomenon termed cardiac chronotropic regulation” (Robberts 1996, Page 144). Thus clearly an increase in heart rate when exercising will lead to an increase in cardio output, this is supported by Wilmore and Costill “when you exercise, your heart rate increases directly in proportion to the exercise intensity”. (Wilmore and Costill 2004 page 224) With regards to this experiment and the increase in work rate and the gradual increase in heart rate observed this is backed up by (Freedson and Miller 2000; Robergs 1996) “moderate through vigorous heart rate increases linearly and proportionally with the intensity of movement and the volume of oxygen consumed.” An important factor relating to the first heart rate and VO2 taken is that other factors may effect the subjects, for example stress, fluid levels and digestion, digestion due to parasympathetic. VO2 is the volume of oxygen consumed per minute. Recent research “has shown that changes in plasma volume are highly correlated with changes in stroke volume and VO2 making the training-induced increases in plasma volume one of the most significant training effects” (Wilmore and Costill 2004 page 287). With regards to the respiratory system the reason its function is not limited is due to a greater ventilation capacity than cardiovascular function.
The differences in Pulmonary Ventilation is vast. “in untrained subjects maximal pulmonary ventilation typically increases from a beginning rate of about 100 to 120 L/min to about 130 to 150 L/min or more following training” (Wilmore and Costill 2004 page 287). However in extremely well trained athletes it may exceed 240L/min. The reasons for this vast change are “increased tidal volume and increased respiratory rate at maximal exercise” (Wilmore and Costill 2004 page 287). The inspiratory muscles are also important as training these can help with better performance. Dispite this being the case Wilmore and Costill (2004)conclude that “in highly trained person’s adaptation the pulmonary systems capacity for oxygen transport won’t be able to meet the demands of the limbs and the cardiovascular system” (Wilmore and Costill 2004 page 287). In other words even if you are unbelievably fit there will still be physical limitations. When this takes place in this case it effects ‘arterial oxygen saturation’ in fact it gets lower “decreases by 96%” (Wilmore and Costill 2004 page 287).
A factor that will have effects all subjects is their lactate threshold. In a trained athlete lactate will still be produced but at a later stage than id they were untrained and the level of lactic acid will often be lower as the body is able to deal with it better.
The latter stages of the experiment were seen to be more important as it is where breathing is intensified and a higher oxygen consumption occurs, a theory backed by Adams 2002 pg 186, “latter stages of the exercise protocol is when maximal oxygen consumption occurs.”
The experiment was approved by the Durham ethics committee and all 7 male subjects signed a consent form. All subjects in the experiment are young ranging from 18 to 21 and thus age is not a deciding factor in the maximal heart rates.
Resting heart rate from a polar N23 heart rate monitor and VO2 from a Harvard Douglas bag were recorded as well as weight and age. Subject were put on a hp cosmos Germany 401 treadmill on a set gradient ofâ€¦ subject steps on to the moving treadmill and the stop watch was started. In the last minute of every 3 minutes the mouth piece was attached to the subject and oxygen excretion for the minute was collected. The subject shouted out the intensity on a Borgs 6-20 RPE scale. At the end of every 3 minutes the intensity was increased. This protocol was continued until exhaustion. The exact time of stopping was then recorded.
Four minutes after exhaustion blood is taken in order to calculate the subjects lactic acid levels. 1 litre of expired air was then removed in a small Douglas bag and put into the Servomex 1440 Cranley medical uk gas analyser for levels of oxygen and carbon dioxide. Original Douglas bag is attached to a dry gas analyser and measures the volume of expired air. The 1 litre earlier removed is then added to this total.
Figure 1: A bar chart displaying means and standard deviations of the relationship between Heart rate and VO2.
Figure 2: Bar chart displaying means and standard deviations of the relationship between work rate and heart rate.
Figure 3: Bar chart displaying mean and standard deviations of the relationship between VO2 (ml.kg.min) and work rate.
It is clear that the data’s showing a strong positive correlation as hypothesised in Fig 1. An increase in work rate means an increase in both heart rate and VO2, “When exercise is performed at a given work rate which is below lactate threshold (LT), Oxygen uptake increases exponentially to a steady-state level”( Xu F; Rhodes E.C. 1999).Fig 2 which is showing the relationship between work rate and heart rate is precise in displaying the increase in heart rate directly to work rate, it should be noted that “When exercise is performed at a work rate above LT, the Oxygen uptake kinetics become more complex. An additional component is developed after a few minutes of exercise. The slow component either delays the attainment of the steady-state Oxygen uptake or drives the Oxygen uptake to the maximum level, depending on exercise intensity” ( Xu F; Rhodes E.C. 1999).
Fig 3is displaying mean and standard deviations of the relationship between VO2 (ml.kg.min), and work rate, it is to be expected that if heart rate increases due to work rate then VO2 will also do the same as if it didn’t then the heart would not be able to either.
Despite this there are still contradicting theories, Adams also concludes that there are other factors that need to be accounted for, “other factors such as running economy and the ability to use a high percent of the maximal oxygen consumption (fractional utilization) and ventilator threshold also the important indicators of success in aerobic performance.” (Adams page 202). An expectation of further studies with fractional utilization of VO2 and time as well as ventilator threshold. It must also be noted that oxygen consumption is dependent on sex and age, “maximal oxygen consumption is higher in men than women, and in younger adults than in older adults.” (Adams pg 202).
Xu and Rhodes believe there is a slow component during intensive exercise, they go on further and speculate some of the possible causes, “The possible causes for the slow component of Oxygen uptake during heavy exercise include: increases in blood lactate levels, increases in plasma epinephrine (adrenaline) levels, increased ventilatory work, elevation of body temperature and recruitment of type IIb fibres” ( Xu F; Rhodes E.C. 1999). These are clearly all contributing factors however it is the recruitment of IIb fibers that Xu and Rhodes attribute most to an incrased need for oxygen, “During high intensity exercise an increase in the recruitment of low-efficiency type IIb fibres can cause an increase in the oxygen cost of exercise. A change in the pattern of motor unit recruitment, and thus less activation of type IIb fibres, may also account for a large part of the reduction in the slow component of Oxygen uptake observed after physical training.” ( Xu F; Rhodes E.C. 1999). I would expect more research focused on this factor in order to examine why there is a need for such a high percentage “86%”( Xu F; Rhodes E.C. 1999) of oxygen uptake slow component obtained from the limbs and more particularly IIb fibers.
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