Foods, fuels and energy systems
1 a Performers are able to work above 100% VO2 maximum when the extra energy is provided anaerobically. This typically involves use of the LA system more so than the PC system, because the PC system would have been depleted.
b Performers can increase the time they spend working anaerobically by improving their lactic acid tolerance. This may occur when training causes lactic acid to accumulate to near maximal levels, followed by a 3–5 minute recovery and then a repeated anaerobic bout resulting in ‘lactate stacking’. Training the LA system in this way will improve its energy transfer capacity and allow longer periods of work to occur above 100% VO2 max.
2 a The interplay of the runner would be different from that of Fig 4.19 because the 400 m runner does not work maximally from the start of the race.
b The energy system contribution would be different for a cyclist performing at 95% of their VO2 maximum. The trends/shape of the energy system graphs would be the same, but the ATP-PC system would deplete slower, and the LA system would contribute slower and peak later, as would the aerobic energy system.
3 Fats are not our preferred exercise fuel because they require more chemical reactions to release energy than do carbohydrates (slower release) as well as requiring more oxygen to resynthesise ATP (less available to working muscles).
4 a A higher lactate threshold is advantageous because it allows performers to:
· work at a higher intensity before starting to accumulate lactic acid (delays this fatiguing factor)
· use their aerobic system for longer to provide aerobic energy (no fatiguing by-products)
· increase their glycogen and glycolytic enzymes.
b By increasing her/his lactate threshold, the performer is likely to have greater contribution from her/his aerobic system for a larger part of the event /activity.
c Intermittent anaerobic training may contribute to increases in a person’s lactate threshold by shifting towards the recruitment of fast-twitch muscles. This typically happens during high-intensity short-interval training. The recruitment of these fibres will shift energy metabolism from mitochondrial respiration (aerobic system) more towards anaerobic glycolysis (LA system), which will eventually lead to increased lactate production.
5 The aerobic system contribution is different for each of the activities because the more intense the activity (90 sec all-out cycling compared with 800 m running and 1500 m running respectively) the lower the overall contribution from the aerobic energy system. All three activities have a similar anaerobic energy release with greater contribution from the aerobic energy system for longer-duration events.
6 a i Athletes can increase their PC store by training due to increased muscle size (especially fast twitch fibres) – increased muscle size will allow more PC to be stored.
ii Athletes can increase their PC store by diet manipulation such as creatine supplementation, which may also lead to increased amounts of PC being stored at muscles.
b A person able to use their ATP-PC system for longer will be able to run a faster time and not fatigue/slow until later in the race than someone who cannot. The longer the ATP-PC system can be used during a 200 m sprint the more energy that can be released from this chemical fuel and the quicker it can reach muscles for contraction. The LA system will require more reactions to liberate energy and can result in fatiguing by-products.
7 a Plasma glucose can be increased by consuming carbohydrates or glucose-rich foods. A rise in plasma glucose stimulates insulin release which in turn promotes glucose entry into cells in an effort to lower the blood glucose levels. This should be avoided immediately before exercise because it means that the body will use glucose early on in the event and may ‘run out’ in the later stages of the endurance event.
b Plasma glucose levels can be maintained during physical activity by consuming (typically soluble) glucose during the event/exercise. This is usually carefully monitored and well rehearsed, to avoid the sharp increases that will lead to insulin being released and glycogen being used. This will allow greater use of glucose as a preferred fuel and slow the reliance upon fats to provide energy.
c Diabetics should always consult their doctor or specialist and discuss exercise demands on their diabetes and how to best manage the two. Some recommendations include:
· Avoid exercise if fasting glucose levels are >250 mg/dl as ketones are likely to be present.
· Wear diabetes identification.
· Be sure to check the blood glucose levels before and after exercise (if practical, get a reading during the half-time break and adjust accordingly). Check it one hour before, as well as immediately before exercise, so you can tell which way your blood glucose is heading.
· If your game occurs a long time after a meal, be sure to have a snack that’s high in carbohydrates before starting the game. Ingest added carbohydrates if glucose levels are less than 100 mg/dl (soluble preferable).
· Carry some carbohydrate food with you while exercising (glucose tablets or lollies in your pocket), in case you feel like you’re starting to ‘crash’, or place them on the side of the hockey field.
· Drink lots of water before, during and after the game.
· Make good use of the interchange bench for recovery.
· Avoid overheating and elevated body temperatures (wear light clothing, use wet towels, ice vests, etc.).
8 a Mitochondria and glycolytic enzymes are both important in the complete breakdown of glucose and aerobic production of ATP. Any aerobic training method will see these increase at the cellular level, e.g. LSD, Fartlek, continuous.
b Glycolytic enzymes speed up the beak down of glucose and this is vital even under anaerobic conditions to release energy via the LA system.
c Maintaining a high aerobic base will greatly assist in the recovery from training bouts. It will assist in the removal of metabolites and possibly increase the rate at which CP is restored.
9 a Muscle lactate has doubled due to increased use of the LA system to provide energy.
b CP depletion after 100 m approx = 40%; after 200 m approx = 60%;
after 400m = 89% depleted
CP has a finite store in the muscles. After relying on the ATP-PC system heavily in the first 200 m, this continues to supply energy, but to a lesser amount, as it becomes more and more depleted in the second 200 m of the race and more energy is derived from anaerobic glycolysis.
c i At the end of the 400 m race, ATP is depleted by approximately 1/3 that of CP.
ii The difference in ATP and CP is due to the fact that ATP is being broken down and re-synthesised at the same time, whereas CP needs a period of rest/recovery to be re-synthesized.
iii Muscle lactate readings give a more immediate indication of lactic acid levels than readings collected from the blood stream, which is why physiologists prefer this method. The body produces lactic acid and consumes it at the same time. The heart, liver, kidneys and inactive muscles are all locations where lactic acid can be taken up from the blood and either converted back to pyruvic acid and metabolised in the mitochondria or used to re-synthesize glucose at the liver. Based on concentration gradients, lactic acid diffuses into these cells from the circulatory system (moving from high to low concentrations). If the rate of diffusion of lactic acid equals the rate of production or appearance in the blood, then blood lactate concentration stays constant. When the rate of lactate production exceeds the rate of diffusion/loss, lactic acid accumulates in the blood volume, then we see the Onset of Blood Lactate Accumulation (OBLA).