water Flashcards
functions of water
- helps transport nutrients and waste products in and out of cells and is necessary for all digestive, absorption, circulatory and excretory functions.
- regulating body temperature
- all enzymes are water-based
- most energy-releasing reactions occur in the body’s watery tissues
- water protects the body’s joints, organs and other tissues
- water suppresses the appetite to help combat over-eating
- most hormones secreted from glands contains a large portion of water.
dehydration
a loss of bodily fluids equal to or greater than 1% of body weight and can be classified as mild, moderate and severe
on average 250 ml is lost on a daily basis through breathing alone.
a 3% loss in total body water will result in
- reduced blood plasma volume = reduces blood pressure and impedes cardiovascular performance.
- decreased kidney function
- decreased blood flow to the skeletal muscles = reduces exercise performance
- reduce blood flow to brain = decreases motor function and concentration levels & headaches
- increased risk of constipation
- reduced metabolic rate because the efficiency of all energy-generating and releasing processes will be suppressed.
5% loss of water
heat exhaustion (can often require medical attention)
7% loss of water
brain function is severely impeded, which regularly results in hallucination and an inability to focus
10% loss of water
heat stroke - if sustained for any great length in time can lead to death
daily water loss through urine
1.2 litres
daily water loss through faeces
0.75 litres
daily water loss through skin evaporation
0.4 litres
daily water loss through respiration
0.15 litres
total daily water loss
2.5 litres
factors affecting fluid loss
- individual biological variance (body size, genetics etc)
- altitude (higher altitudes accelerates water loss)
- acclimatisation to the environment
- exercise intensity and duration
- environmental temperature
- other dietary factors, especially diets high in caffeine, alcohol and protein
signs of mild dehydration (1%)
- sluggishness
- general fatigue and tiredness
- headaches
- infrequent urination (less than 3-4 times a day)
- dark brown coloured urine
signs of moderate dehydration (3-5%)
- loss of appetite
- heat sensitivity
- constipation
- light-headedness
- nausea
- joint ache
- liver dysfunction
severe dehydration (>5%)
- reduced kidney function
- greater risk of kidney stones
- dry and wrinkled skin
- inability to urinate
- weak and rapid heart rate
- seizures
- cold extremities, especially the hands and feet
- low blood pressure
fluid intake guidelines
- approx 2-2.5 litres a day
- one litre of fluid for every 1000cals consumed
- it is possible to get 20% of required daily fluid from food
fluid guidelines for exercise
pre-exercise = 0.5 litres of cold water 2 hours before exercise
during exercise = 120-180ml of cool water every 15 mins
post exercise = 0.5 litres of cool water for every 1lb of body weight lost
electrolytes
electrolytes are minerals and salts that have the capacity to conduct electrical impulses throughout the bodily tissues.
common electrolytes = sodium, potassium, chloride, calcium and bicarbonate
hyponatraemia
in cases where the exercise duration and environment causes considerable water loss, simply drinking water alone can significantly decrease exercise capacity. as more water is consumed, the more diluted sodium levels in blood become - this can lead to hyponatraemia
symptoms include = nausea and vomiting, headache, confusion, lethargy, fatigue, appetite loss, muscle weakness, spasms and cramps
sports drinks
the consumptions of fluids containing sugars and salts will affect the absorption rate from the intestines; this is referred to as the osmolality of the drink.
drink with high osmolality are hypertonic
drinks with low are hypotonic
drinks with same osmolality as the body’s fluids are isotonic.
hypertonic drinks
contain more glucose than the body’s fluids (greater than 8g p/100ml) and so their absorption from the intestines is slower than water alone.
good for post exercise. can be consumed during prolonged exercise in conjunction with isotonic drinks to help maintain stable blood glucose levels and replace lost fluids.
can be used to supplement daily carbs intake to help replenish muscle and liver glycogen.
high sugar = increase risk of tooth decay
hypotonic drinks
contain less glucose than bodily fluids (4g per 100ml) and so their absorption rate is much greater than that of hypertonic drinks.
best suited for during exercise because result in faster rehydration.
while they do contain some glucose, it’s unlikely they will have any impact on athletic performance
isotonic
drinks contain same amount of glucose as bodily fluids (between 4 and 8 g p/100ml)
absorption from the intestines is faster than just water.
contain a significant amount of glucose, they can also be useful as a fuel during prolonged exercise.
homemade sports drinks
isotonic = 200ml of orange squash (concentrated orange), 1 litre water and a pinch of salt hypotonic = 100ml of orange squash (concentrated orange), 1 litre of water and a pinch of salt hypertonic = 500ml of orange squash (concentrated orange), 1 litre of water and a pinch of salt
maltodextrin
a food additive commonly used in sports drinks to enhance their effect on blood sugar
sports drinks nutrition labels may only display maltodextrin and not glucose/sugar - but they still have a potent affect on glucose in short term
diuretics
a substance that encourages water loss from the body. the most commonly consumed are caffeine-containing drinks like coffee, tea, alcohol and carbonated drinks
excessive and sustained consumption of diuretics can result in headaches, reduced cognitive performance, joint pain and kidney performance
caffeine
can increase endurance, concentration and mental alertness.
the long term effects are the opposite - as it is a diuretic and excessive consumption will likely result in dehydration
other side effects = anxiety, gastrointestinal disturbances, insomnia, tremors and abnormal heart rate.
many exercisers use caffeine as a means of reducing body fat - when taken in significant quantities (equal to 1.5-3.5cups of filtered coffee) it results in the secretion of adrenaline which helps to mobilise fatty acids from the body’s adipose tissues
has also shown to improve athletic performance by 7%, and appear to be even greater when consumed in tablet form.
alcohol
a nervous system depressant and a diuretic
Dep of Health = 2-3 units p/day for women and 3-4 units for men
densely packed with energy ~ 1g=7kcals
takes the liver 1 hour to process one unit of alcohol
sclerosis of liver = alcohol abuse
monitoring hydration status
urine colour - hydration level clear = hyper-hydrated very pale yellow/pale yellow = euhydrated yellow = mild dehydration dark yellow = dehydration orange or brown = extremely dehydrated
