Lecture 2 (2) - Water

Question 1

Types of hypohydration (2 reasons why it occurs)

Answer 1

• Pre-existing hypohydration: When someone starts a bout of exercise in a state of hypohydration. Any dehydration that occurs in this exercise bout, will accrue on top of this hypohydration. Could be done deliberately for weight requirements in a sport e.g., boxing. Or when an athlete conducts multiple sessions in a day and are still dehydrated from the 1st
• Exercise-induced hypohydration: hypohydration that occurs in the exercise bout itself. Lose more fluid than is taken in.

Question 2

Involuntary dehydration

Answer 2

• Hypohydration produced by fluid restriction and exercise
• 5km treadmill performance test to induce hypohydration
• ~6% impairment in 5km performance (time to complete the 5km was quicker when the athletes were euhydrated compared to hypohydrated) – Flemming and James 2014

Question 3

Environmental temperature

Answer 3

• 4 groups of ppts: did exercise at either 10, 20, 30, 40 degrees C
• Each ppt did 2 trials: euhydrated and hypohydrated
• 30 degree and 40 degrees caused a significant drop in performance – dehydration has more of an effect on the performance the hotter the conditions get
• Greater environmental temperature exacerbated the negative effects of hypohydration
• When exercising in the heat, skin blood flow is increased so more blood goes to the periphery to allow sweat to be released. Less blood is available for muscles and brains etc so maintaining exercise is harder- skin perfusion/ vasodilation.

Question 4

Strength performance

Answer 4

• 24hr complete fluid restriction with maximal strength test before and after
• Maximal voluntary force production reduced with hypohydration
• Hypohydration and fatigue reduces ability to stabilise joints

Question 5

Skill performance

Answer 5

• 1hr exercise in the heat with/ without fluid replacement – induced hypohydration by ~6%
• 6 overs bowled and shuttle run test before and after
• Hypohydration impaired: Line and length, but not speed of bowling
• Hypohydration impairs skill performance across a variety of different sports including cricket
• Shuttle run performance deteriorated more in the hypohydrated trail.

Question 6

Exercise induced dehydration:

Answer 6

Exercise-Induced Dehydration triggers:
Decrease in Plasma Volume, Increase in Plasma Osmolality, Increase in Thirst, Decrease in Mood

Decrease in Plasma Volume: Reduces cardiovascular (CV) function, which in turn impacts body temperature regulation.

Increase in Plasma Osmolality: Leads to higher thirst, increased muscle glycogen use, and elevated body temperature.

Higher Thirst and Lower Mood: Both contribute to an increase in rate of perceived exertion (RPE).

Higher Muscle Glycogen Use and Elevated Body Temperature: Further strain the body, enhancing RPE and contributing to impaired performance.

Impaired Endurance Performance: Ultimately, all these factors (reduced CV function, higher body temperature, increased muscle glycogen use, and RPE) culminate in reduced endurance capacity.

Metabolic effects: Hypohydration cause muscle glycogen use to be higher – greater reliance on anaerobic energy metabolism more glycolysis and less pyruvate into the krebs cycle

Question 7

Limitations with current hydration research

Answer 7

1) Subjects are not blinded from the study intervention or aim – placebo effect, perceptions influence performance, no placebo effect?
2) Typical methods used to dehydrate subjects in studies are unfamiliar, uncomfortable and outside normal practice

Question 8

Blinded hypohydration

Answer 8

• Infuse fluid into stomach (through the nose) without ppts knowing to blind their hydration
• Exercise felt harder (RPE) when hypohydrated
• Did expectation effects influence performance outcomes? Unblind group had 10% drop in performance whilst the blind group had an 11% drop (not statically different).
• Shows the effects of hypohydration are real (not placebo)

Question 9

Faster athletes are more hypohydrated?

Answer 9

Greater body mass loss (indicative of hypohydration level) is associated with faster racing times – not compatible with the idea that hypohydration impairs performance. Conflict between lab and field data
Faster pace: More metabolic heat, higher sweat rate, Less comfortable to drink when running fast, Less time available to drink

Slower pace: Less metabolic heat, lower sweat rate , More comfortable to drink, More time available to drink

Question 10

Unfamiliarity with hypohydration:

Answer 10

• Got ppts more used to being hypohydrated (acclimatised)
• After familiarisation trails of being hypohydration the performance difference between euhydration and hypohydration diminished.
• There is some level of habituation that can happen for hypohydration
• Before acclimatisation RPE was significantly higher when hypohydrated
• Marathon runners can deal better with the effects of hypohydration

Question 11

Lecture summary:

Answer 11

• Hypohydration (at least if unfamiliar) impairs performance
• Familiarisation attenuates this impairment
• Endurance training might have the effect of repeatedly familiarising athletes with hypohydration?
• During running, hypohydration is theoretically ergogenic as it reduces the weight to be carried. If you are hypohydrated you are lighter which could be advantageous for running
• Does this explain why competitive endurance athletes can finish races with hypohydration equivalent to 8-10% body mass?
• Hypohydration certainly seems to impair exercise more at higher temperatures, likely due to changes in cardiovascular/ thermoregulatory function