By Richard Gardner

Introduction

Aerobic Exercise
In the current climate sports and exercise involvement has advanced from the lycra clad, home based fads of the early eighties to a high tech lifestyle backed by a multi-million pound, global enterprise. With the range of facilities becoming broader and access to them less trouble-free, participation has never been simpler.

Although the range of products and different systems on the market can seem daunting, it has become accepted that for a physical exercise program to be truly effective it has to consist of the following elements: flexibility, aerobic conditioning and resistance training. In this project I will be concentrating purely on aerobic conditioning. Aerobic training involves rhythmical body movements over a period of time, doing so will increase the heart rate and also the amount of air the lungs inhale.

"Use a variety of cardio respiratory activities to challenge the heart and lungs", (Brooks, 1998, p13).

As skiing is both enjoyable and relaxing, whilst at the same time being less monotonous than other aerobic activities - running on a treadmill, cycling an exercise bike - I want to determine how effective it is as an aerobic workout. Skiing is undoubtedly a high activity sport that requires a high level of aerobic fitness in order to perform at the highest level, however, is it effective when employed as a supplemental exercise for an existing training program?

Athletes calculate the effectiveness of an aerobic workout by exercising at a percentage of their maximum heart rate.

"Exercise is beneficial to your heart only if it achieves between 60 and 90 percent of your maximum heartbeat rate", (Fiennes, 2000, p46). Or

"(60%-85%) to determine your training heart rate zone", (ivillage, online, 2002)

Hypothesis
In this project I wish to perform an experiment that challenges the heart rate during a dry-slope skiing session. The primary objective for this research is to ascertain how much pressure this activity places on the circularity system and whether or not it works the heart at an ideal aerobic capacity - within the 60-90% of maximum heartbeat rate defined by Fiennes. I aim to use two skiers and monitor their pulse rate at regular intervals during the ski session with a third; non-exercising party acting a control. I am also to include a brief health questionnaire for all parties to fill in to highlight any variables within the group.

Description of techniques
All three subjects for the experiment agreed to complete a simple health questionnaire, this was included to provide a brief overview as to their level of fitness. The subject's chosen were all young none-smoking males of similar age. Both skiers were also picked due to their high involvement in the sport, as although a beginner might find it an aerobically demanding exercise, the same benefits might not apply if equipped with skill and experience.

It was decided that the best way to chart the findings would be to divide the experiment equally. Due to the nature of skiing it seemed more convenient to split this by a set number of ski runs - 4, 8 and 12 - rather than with the use of a timer.

Once the resting pulse rates had been noted, the experiment was underway and both skiers commenced their runs. As the exercise progressed, various changes took place. The skier's appearance - face becoming more flushed - and breathing, quicker, shallower both differences became more apparent as the ski runs progressed. Even without testing pulse, the effects of exercise were quite apparent. Both skiers were working all major muscle groups and to do this requires energy, to create the energy, the muscles in turn require oxygen. The oxygen is brought into the body via the lungs - hence the increase in breath-rate - it then has to travel to the muscles. Oxygen is circulated by the blood supply and is pumped throughout the body via the heart. The flushed appearance on the faces of the skiers comes as a result of the increased blood flow and need for oxygen.

The art of skiing comes from a simultaneous upper and lower body movement; to maintain a controlled speed both skiers must turn constantly as they descend the slope. During each turn, the legs work to keep the run and direction steady but whilst this is happening, the upper body works to maintain overall balance. It is from this combined effort that works the muscles and in turn challenges both heart and lungs to provide the increase in oxygen required.

During the course of the experiment it became apparent that skier B decided to put more effort into the runs. Whereas skier A took a more leisurely approach, B was pushing harder all the way and this is reflected in the times of his runs.

By the closing stages both skiers had also started to perspire around forehead and cheeks. As the muscles are worked harder, they become hotter and need to be cooled down. Sweating is the bodies natural cooling system, distributing water to this skin - subsequently if this water isn't replaced the person will become dehydrated thus professional athletes constantly drink fluids to keep the body in balance.

Once the runs are completed and the final results are taken, both skiers appear relatively fatigued and short of breath. Throughout the readings, the control remained resting and their results remained almost identical whereas the skiers had interesting differences during the course of the exercise. Even without the aid of results it is obvious they have exercised at some aerobic capacity - sweating and breathlessness - but will it fall within the ideal model established earlier?

Summary of Results / Data
The results were collected after 0, 4, 8 and 12 ski runs respectively, the time into the exercise for each reading was also noted. For the pulse rate recordings, the amount of pulse beats was taken for 10 seconds and then multiplied by 6 to give an estimated BPM (beats per minute). This was performed 3 times after each set of runs to get an average rating. For each set of results, the skiers were labelled A and B, whereas C represents the stationary control.

Skier A

Skier B

Control C

Table 1: Results of experiment

Maximum Heart Rate
To work out whether the skiers were working at an ideal aerobic capacity their maximum heart rate first has to be established.

'The intensity of aerobic workouts is dictated by your maximum heart rate (MHR) which is approximately 220 minus your age', Men's Health, 2001, p 121.

Given that skier A is 21 and skier B 20, the following table works out their MHR, 60% of their MHR and 90% of their MHR respectively.

Table 2: Maximum heart rates for Skiers

These statistics now need to be gauged against the pulse rate recordings; the following chart demonstrates this.

Table 3: Summary of results

Analysing the results

Both skiers registered a sharply increased pulse rate after the first set of four runs; in fact skier B had already reached 60% of his MHR. In contrast to this it took an estimated 7 runs before skier A reached the 60% minimum pulse rate required for effective aerobic conditioning - an estimated time of around 12 minutes.

Once B had reached 60% his pulse rate stayed around the minimum for the remainder of the experiment - dipping slightly under this target by the final readings.

The pulse readings for skier A, increased steadily above the minimum effort required and seemed to peak after 8 ski runs and a time of 18 minutes. Around this point, skier A would have been working at around 64% of his MHR.

Over the 25-30 minutes, the average pulse rate indicates that both skiers were working their hearts at around 52% of their MHR - around 105 beats per minute.

Conclusions reached from the results

The results gained from both skiers seem to indicate that although dry-slope skiing does work the heart and lungs at an aerobic capacity, it is not enough to be deemed effective as a stand-alone workout. The average pulse rate over the time elapsed is below the recommended minimum.

Even though skier B pushed quite hard during his runs, his heart rate only just touched the minimum amount of effort required to challenge heart and lungs effectively. Skier A did reach a level of exercise intensity that would train heart and lungs adequately, this was not reached until around fifteen minutes though by which time he could have almost finished an effective treadmill workout. The variable weight of both skiers can also be taken into account, skier B was lean and the ideal weight for his height; skier A was overweight though and this would reflect the increased heart rate over skier B.

To conclude I think that dry-slope skiing is a fun activity and can be employed into an overall health plan. It cannot be used solely as an aerobic workout though as it does challenge the heart and lungs enough.

Discussion

Exercise physiology

The most apparent effects of exercise upon the human body are: increased heart rate, increased breath rate, reddened skin and sweating. To look at why this happens it is important first to look at the process of muscular movement.

To carry out any form of physical activity muscular movement must occur. To move different body parts, muscles must expand and contract according to need. For this to happen the muscles themselves need a supply of energy. The form of energy the body requires to shift muscles is called ATP (adenosine triphosphate). ATP is a chemical and there are three separate systems the body uses to access it:

- The ATP/CP system is ATP already present in the muscle cells. This is employed when the body requires instant energy such as bodybuilding or 100m sprints. The ATP system is anaerobic meaning it does not require oxygen for the formation of energy.
- The Glycotic system is synchronized when energy is required for activities lasting between 10 and 60 seconds for example, 200-400m sprints. Glycosis converts glucose molecules to ATP, producing 2 ATP molecules for each glucose molecule. This works only for short-term exercises (lasting up to a minute) as glycosis produces lactate ions that will eventually impair muscular contraction. The system is useful as it is readily available and also anaerobic.
- The Aerobic system is the energy system the body employs for physical activities in excess of one minute. The aerobic system needs an intake of oxygen but is much more efficient at producing ATP - 36 ATP molecules per glucose molecule. The aerobic system works by breaking down stores of fat and carbohydrate to produce ATP. Most sports use the aerobic system and the need for oxygen is responsible for increased breathing and heart rates.

When muscles contract and exert the pressure required to perform exercise, initially they use the first two energy systems to produce the energy required. To carry on though the muscle cells have to get energy through breaking down the fat and carbohydrate stores around the body and adopt the aerobic energy system.

The breakdown of lipid and carbohydrate molecules occurs within cells and is referred to as cellular respiration. To understand how the aerobic system produces energy it is best first to look at the glycotic system. This system creates energy through glycosis, breaking down glucose molecules (glycosis occurs in the cytoplasm of the cell). This is achieved through a series of enzyme-controlled reactions with the end product being 2 ATP molecules and also a supply of pyruvic acid. Without the presence of oxygen this is then converted to lactic acid that can impair muscular performance.

The aerobic system employs glycosis also. The difference is that with the aid of oxygen, the pyruvic acid is converted to acetyl coenzyme A and enters a tiny organelle within the cell called the mitochondria. Once inside, the molecules enters what is known as the Krebs cycle, "The Krebs cycle is a very complex series of chemical reactions", (Brooks, 1998, p 78). The Krebs cycle breaks down the molecules even further before releasing them through what is called the electron transport chain (the inner membrane of a mitochondria). It is here where ATP molecules are released back into the cell. Once cellular respiration has taken place, ATP enters the blood stream and travels to where it is needed (in the case of exercise, muscle tissue).

The process of cellular respiration generates a high concentration of carbon dioxide within the blood supply. Tiny chemoreceptors located in the aorta of the heart detect this and notify the respiratory and cardiovascular centres (located in the medulla oblongata of the lower brain). This has two specific reactions that work in harmony. Firstly the respiratory centre sends nerve impulses that pass down efferent nerves to the intercostal muscles and diaphragm. Secondly the cardiovascular centre sends nerve impulses down the sympathetic nerve to increase heart rate. Upon receiving an impulse, the intercostal muscles pull the ribcage upward and outward and at the same time the diaphragm contracts, increasing the capacity of the thoracic cavity. This process is called inspiration. The lungs are held to the ribcage and diaphragm by two pleural membranes and the process of inspiration sucks air into the lungs. Once inside the lungs, the air moves into a series of tiny sacks called the alveoli (via the bronchus and bronchioles). See fig 1.

Fig 1: Inspiration of the lungs

As air enters the alveoli, oxygen diffuses across the fine membrane and enters the bloodstream. When inspiration is complete, the intercostal muscles relax and the diaphragm pushes back up against the lungs. "Relaxation of the breathing muscles allows the springy, elastic tissues of the stretched lungs to return to their naturally contracted position", (Microsoft Encarta, Online, 2002). This process is called expiration and during expiration carbon dioxide diffuses from the blood supply into the lungs; this is then expelled from the body through exhalation.

The blood, now with a high oxygen concentration, enters the heart through the pulmonary veins. The heart is a four-chambered pump split into two halves. The right side takes the deoxygenated blood supply from around the body and pumps it to the lungs to be oxygenated. The left side receives oxygenated blood from the lungs and pumps it back around the body. Each side consists of the following: an atrium, a ventricle, an atrio-ventricular valve and semi-lunar valves. (See fig 2).

Once the heart receives an impulse from the cardiovascular centre it speeds up the rate of the heartbeat. The heart beats through what is know as the cardiac cycle. An electrical impulse is started in an area called the sino-atrial node - located in the right atrium. This is then received by another node, the atrio-ventricular node, which transfers the impulse to the septum through fibrous strands called the bundle of His. The action of this impulse is to make the muscles of the heart expand and contract.

Fig 2: The structure of the Heart

The first stage of the cardiac cycle is called the atrial systole. During this stage the both of the atrium contract, the atrio-ventricular valves open and blood enters the ventricles.

The second stage, ventricular systole is when the ventricles contract. At this stage the atrio-ventricular valves close and the semi-lunar valves open. This forces blood out of the heart via the pulmonary arteries and the arch of aorta.

In the third stage, atrial diastole, the muscles surrounding the atrium relax and both atriums are filled with blood from the superior and inferior vena cava and pulmonary veins.

The final stage of the cardiac cycle is called the ventricular diastole. The ventricles relax and prepare to fill once again in a new cycle.

When exercising, both breath rate and heart rate increase. This is due to the increased respiration of oxygen within cells. Through regular aerobic exercise, the heart (like any other muscle) will grow in size. This increases the stroke volume (the volume of blood the heart can take in any cycle) and this means the heart has to work less to get more supply the body with the blood it requires. The ideal aerobic training zone to condition the heart correctly is between 60 and 90% of maximum heart rate as defined by Fiennes. Training at this capacity is sufficient to challenge the heart and over time improve cardiovascular fitness.

Another benefit of training aerobically is fat loss. By exercising we increase the amount of ATP required for muscular movement. ATP is a chemical created in an oxidised environment through the breaking down stores of carbohydrate and lipid molecules. "Lipids cannot be used for short term exercise but they can be used to fuel aerobic exercise", (Boyle, Indge, Senior, 2001, p 195).

As we exercise, blood is pumped faster around the body - this is why aerobic exercise makes the skin go red. When muscles are working hard they also heat up, by sweating we not only expel excess water built up through cell respiration but also the passage of water through the skin tissue acts as a cooling agent.

Appraisal of Work
The nature of dry-slope skiing may have hampered the effectiveness of this experiment. Whereas downhill or alpine skiing takes place over a lengthy time period, limited slope space means that ski runs are interrupted every few minutes and a lengthy wait occurs as the skier is transferred back to the top of the dry ski slope.

Although in saying that, the reason for the experiment was to test the effectiveness of dry slope skiing as an aerobic workout. I believe in this respect it highlighted the weaknesses and showed that it is not reliable if you were looking to exercise within 60-90% of your maximum heart rate.

Whilst dry-slope skiing should only be viewed as a leisure pursuit, it would be very interesting to conduct a similar experiment around downhill skiing. The length of time actually spent skiing and the lower concentration of oxygen at a higher altitude would I believe produce drastically different results.

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Resources

Books
Boyle, Indge and Senior. (2001). Human Biology. London: Collins.
Brooks, Douglas S. (1998). Program Design for Personal Trainers. Leeds: Human Kinetics.
Fiennes, Ranulph. (2000). Fit For Life. London: Little, Brown & Company.
Mens Health Magazine. (May, 2001 Issue). London: Rodale Ltd.

Internet
Microsoft Encarta. Lungs. [Online]. (URL http://www.encarta.msn.co.uk/find/Concise.asp?z=1&pg=2&ti=761570316) Microsoft Cooperation. Accessed 24 Apr 2002.

ivillage. Fit by Friday. [Online]. (URL http://www.ivillage.com/diet/experts/fitfriday/qas/0,5090,253454_2580,00.html) ivillage.com. Accessed 24 Apr 2002.