Question

Vinnie is a professional road cyclist participating in the 2020 Giro d’Italia, a three-week race nearly 3,600 km in distance with some stages exceeding altitudes of 2,700 m above sea level (i.e., Stelvio Pass, Italy). As the newly hired head of the high-performance team, it is your responsibility to manage his preparation for the event. You must demonstrate to your team a fundamental understanding of physiology, the chronic adaptations expected from his training, and methods that could be implemented to improve the likelihood of success.

1)Your first job was to schedule a VO₂max test for Vinnie to examine his aerobic fitness. After repeating the assessment several weeks later after an intensive training block, you notice that VO₂max has dropped, but there has been an increase in VT₂. Please discuss why VO₂max decreased and what impact both changes will have on performance?

2)Out of interest, you decide to measure Vinnie’s gross mechanical efficiency during cycling (i.e., the ratio of work accomplished to energy expended). You determine that he is 21.9% efficient. Please explain what efficiency is a measure of, where does this value sit within normal efficiency data and why you are unlikely to see values much higher (e.g., 50%)?

3)Within the alveoli, the partial pressure of O₂ is reduced from that measured in the outside air (160 mmHg) to approximately 105 mmHg.

1. What three factors contribute to this reduction in P_AO₂?

What values do you expect to observe in PO₂ and P_AO₂ when Vinnie is cycling at the peak of Stelvio Pass (barometric pressure = 543 mmHg)?

What impact would the change in P_AO₂ have on Vinnie’s performance?

4)

The longest leg of the race is 228 km, during which energy intake is critical. Glycolysis and β-oxidation are processes that break down carbohydrates (i.e., glucose, sucrose, fructose) and fatty acids, respectively.

1. Individually, what is the total ATP yield from one molecule of glucose and one molecule of palmitate?
2. How did you reach these numbers (i.e., substrate yield and use)?

Based on what you know about the yield and speed of these two pathways, do you recommend Vinnie ingest glucose or fatty acids during the race? (Hint, remember the cross-over concept)

5)

You recommend that Vinnie performs altitude training as part of his preparation for the race, a training approach that is novel to him.

1. What physiological changes would you expect in the short (i.e., acute), and long-term (i.e., chronic)?
2. How will the physiological changes influence performance in the short (i.e., acute), and long-term (i.e., chronic)?

6)

During a casual chat with a sport scientist from another team, they suggest preparing “finish bottles” for the longer legs of the race. Along with a dose of painkillers, a “finish bottle” typically contains an ergogenic dose of caffeine (i.e., approximately 3 to 5 mg·kg^-1 of bodyweight).

1. As a sympathetic nervous system stimulant, what acute physiological changes will likely occur following caffeine ingestion at these doses?

Additionally, caffeine has a mild effect at mobilising free fatty acids. Please describe what is meant by mobilisation, and how this may influence performance

7)

Given that the average distance of each leg is 170.5 km in distance, and sometimes undulating in elevation, you understand that fatigue is inevitable. The energy depletion model of fatigue focuses around the concept that depleted substrates are just one source of fatigue, particularly observed in muscle glycogen and phosphocreatine stores.

1. As an aerobic event, why do you expect depletion in glycogen and phosphocreatine?
2. Why, specifically, is it crucial to replenish muscle glycogen stores prior to the next leg?

8)

As the event is soon approaching, parts of Hungary are experiencing a heatwave. Indeed, temperatures may exceed 32° Celsius during the first leg of the race leaving Budapest.

1. Will the ambient temperature have any impact on Vinnie’s performance?

In terms of thermoregulation, what physiological changes are likely to occur during this leg of the race?

Answer 1

1)VO2 max is the maximum amount of oxygen an individual utilizes during intensive exercises. This is measured in milliliters of oxygen per minute per kilogram of the body weight and is used to determine the cardiovascular fitness of a sports person. Any intense training exercise can increase the efficiency of oxygen transport in the body. Training lowers the resting heart rate (HR) and at sub maximal loads the volume of blood pumped into heart is increased at every beat. A test for VO2 max before and after training tests shows a decrease in the value as the reduced resting heart rate results in increased blood flow to heart and thus more oxygen is delivered. This causes increased stroke volume and decrease in the VO2 max. The values depend on many factors such as age, gender, body weight, training methods, altitude etc. O2 levels are low in higher altitudes and so the oxygen consumption decreases in higher altitudes. VO2 max levels are a threshold that shows the ability of an individual to transport oxygen effectively during physical activities. So this can contribute to endurance sports events like cycling. The ventilator threshold or VT is the measurement of intensity of breathing while training, at a point where lactate is accumulated in blood stream because the training increases the lactate in blood faster than it buffers. The first and second levels of ventricular threshold are VT1 and VT2 which differs in the intensity in which the latter has high intensity. When lactate accumulates faster the breathing should be quick as well. When O2 levels are limited then pyruvate is converted to lactate that produces more energy from glucose breakdown. So during intense exercises the maximum intake of O2 is reduced so the lactate production increases and is converted to energy that is utilized during training. But the lactate production may build up in the body faster than it is being used. This increases the VT2. If we do high intensity exercises it can activate the fast twitch muscle fibers that have great speed with less endurance. When the VT2 reaches a point where the fast twitch muscles gets activated, it shows the ability of the exerciser to increase the speed and fitness that is needed for professional sports events.

2)Mechanical efficiency is a measure of a person’s ability to transfer the energy that he consumes into performing any external activities like exercises. This is an important factor which can help understand the metabolic as well as mechanical adaptations while performing exercise especially while training. This can help estimate the efficiency of a particular training routine and also for health evaluations. The gross value of mechanical efficiency is calculated by dividing the mechanical power in watts by exercise metabolic power. The normal values range from 11 to 23%. Vinnie, a professional road cyclist shows an efficiency of 21.9 % which does fit in a normal range. This doesn’t go beyond a certain level of efficiency value because the energy demands during training is decreasing as per the decrease in VO2 and enhanced respiration produces more ATP while the O2 requirement is decreased for the same intensity of training.

3)The decreased value of partial pressure of oxygen compared to outer air partial pressure is contributed by factors such as the rate of oxygen consumption and the production of carbon dioxide, the alveolar ventilation rate and the perfusion rate and the partial pressures of the inhaled and exhaled gases. Partial pressure in alveoli shows approximately 105mmHg. The reason because when O2 is inhaled and entered to lungs it humidifies by upper air path and reduces the PO2 to approximately 150mmHg from the normal value of 160mmHg. Pulmonary capillaries uptakes this O2 inhaled and diffusion of CO2 also affects the partial pressure in the alveoli which is reduced to 105mmHg. This is important because the change in the partial pressure of oxygen in alveoli helps the exchange of gases as the diffusion occurs from higher to lower partial pressures.

4)Total ATP yield from one molecule of glucose is 36 ATP. One molecule of palmitate produces 129 ATP. 2 ATPs from glycolysis, 2 ATPs from the Krebs cycle, and about 34 ATPs from the electron transport chain. 2 ATP are used during the processes and 34 ATPs are gained during the processes. During glycolysis 2 mol of ATP are initially consumed and 4 mol of ATP are ultimately produced. Beta Oxidation of of palmitic acid yields 7 NADH + 7 FADH2 + 8 acetyl-CoA.. Each acetyl-CoA yields 3 NADH + 1 FADH2 + 1 GTP in Krebs cycle thus producing of 3 ATP/NADH and 2 ATP/FADH2 and 131 ATP molecules. 2 ATP molecules are used for initial activation. Thus yields 129 ATP.

The crossover concept is the balanced use of fat and carbohydrates during exercises which depend on the interaction between the intensity of exercise and the endurance of the individual. Initially exercising uses carbohydrates as the main source of energy. But endurance training increases the fat oxidation and decreased sympathetic nervous system activity. So adapting to energy use from fats with higher intensity training the body can favor fat oxidation for the energy requirements. So it is recommended that Vinnie ingest fatty acids during the race.