Physiology

Physiology

Instructions

Read the case study below and place yourself in this scenario, consider all the physiological responses that occur throughout the event and how they are inter related. Then answer the questions at the end, they should NOT be one or two word answers. References are required where appropriate, you have 1500 words to use as you deem appropriate for each answer.

Background:
Competitive marathon running is an endurance event that is physically demanding and requires the runner to sustain an almost constant effort throughout the duration of the event (e.g. ~2:03-2:20; elite males). The marathon requires significant contribution from the aerobic energy systems to fully realize optimal performance. Just as importantly, all physiological systems need to be controlled and regulated so that they function in a coordinated way, they will be in what might be called a ‘steady state’ condition for large periods of the race and homeostasis will be challenged as they [physiological systems] continually adapt to new physiological stresses throughout the race.

Scenario: The race
Imagine you are standing on the start line of the men’s/women’s marathon, the weather is good, there is a clear blue sky and the temperature is 15 °C at the start of the race and is expected to rise to 20 °C by the end of the event. You are nervous, people around you are buffeting you, your heart rate has risen to 110 beats per minute (b.min-1) and you are sweating mildly, breathing 18 times per minute and your tidal volume has increased. The starter is ready, your muscles tense as you brace yourself for the start, the starting signal sounds, you leave line in an almost sprint like fashion to quickly get up to race speed. At the end of the first minute your heart rate is at 186 b.min-1, your breathing frequency is 50 breaths per minute, minute ventilation has increased to 105 L.min-1.

A few minutes later you pass the 1-mile mark, you are running slightly faster than your scheduled race pace and you are aware you need to stick to your own strategy if you want to complete the race in a personal best (PB) time. Over the next 4 miles you settle into your race pace, your heart rate has dropped slightly to 182 b.min-1 and your minute ventilation has stabilized to 115 L.min-1. Your oxygen uptake (VO2) is at 80% of your maximal. You have also started taking on a mixture of water and liquid carbohydrates at feed stations along the route; you do this as often as you can during this important stage of the race. Core temperature has risen to 38.3 °C during these early stages of the race.

You are now approaching the halfway point of the race; you still feel good and are on schedule to beat your PB, you pass through halfway in 1:11:54. Buoyed by this you start to increase your pacing slightly as you have planned to run a negatively split race (aiming for 2:20:00). The air temperature has risen by 2 °C and you have become aware that you are sweating more as your core temperature is also rising, it is now at 38.5 °C. The need to drink regularly now has become more important during the remainder of the race.

With 6 miles to go, you enter the most crucial phase of the race. You feel tired, but are still maintaining race pace. You core temperature is now 39.1 °C and remains at this for the remainder of the race. Your heart rate is now at 185 b.min-1, you focus on the athlete ahead of you to help keep your mind away from the feelings of tiredness during the next few miles.

Into the last mile, you are on schedule to beat your PB, but your legs feel heavy and leaden, your are running at the maximum speed you can, feeling tired and fatigued you keep pushing yourself as hard as you can, your minute ventilation, heart rate and breathing frequency have increased slightly again as you head toward the finish line. With 400 m to go you muster all the remaining energy you have to ‘sprint’ to the finish line.

Across the finish line, 10 seconds under 2:20:00, you have run a new personal best! You stop running – exhausted, you slump to the ground. You gasp for air, still breathing at 58 times per minute, your whole body is aching, and the burning feeling in your legs is starting to ease as your body begins to recover from the final push to the line. You now start to sweat profusely as your body tries to cool itself down; the sweat is dripping off you.

Five minutes later after a slow walk back to race control your heart rate, ventilation rate and VO2 are almost back to normal. Your core temperature is still high and you have lost 1.5 kg in body mass; your legs still feel heavy from your excursions, blood lactate remains elevated, indeed it has risen slightly since the end of the race.

Assessment questions:
(1500 words)

At the start

1. At the start your heart rate, breathing frequency and ventilation have all increased, what is responsible for raising these before you start the race? (20 marks)

One mile in

2. What factor(s) is/are responsible for the increase in core temperature during the initial stage of the race? (20 marks)

Halfway mark

3. What mechanisms are regulating acid base balance during the race? (15 marks)

4. How does drinking fluid alleviate detrimental increases (to performance) in core temperature? (15 marks)

The finish

5. You have stopped running and you are at rest, but your heart rate and breathing frequency are still very high, why is this still the case? (10 marks)

6. Discuss the likely mechanisms of fatigue that can occur during this event? (15 marks)

7. Your average cardiac output for the race was 28.58 L.min-1 and your average heart rate was 185 b.min-1. Calculate average stroke volume during the marathon (give correct units and round to 1 dp)? (5 marks)

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