3 What’s happening in your muscles? In normal conditions our body uses oxygen to fully break down glucose in aerobic respiration:2900 kJGlucose + oxygen energy + water + carbon dioxideDuring hard exercise, muscles use up a lot of glucose to get enough energy.Sometimes not enough oxygen can get to the muscles so anaerobic respiration (without oxygen) takes place and Lactic acid forms.
4 Why does this happen?During vigorous exercise you need a lot more energy and get it by:Breathing deeper and fasterDilated blood vessels deliver more oxygen to muscles (and increased heart rate)When at maximum, body starts to respire anaerobically (making lactic acid), butMuscle fatigue results from a lack of oxygen and a build up of lactic acid.
5 Investigating exercise’s effects on pulse rate Pupil ActivityCopy this table into your notes:Measure your resting pulse rate over 1 minute.Exercise for 2 minutes.Measure pulse rate again.Wait for 2 mins.Measure pulserate again.How has the pulse rate been affected by exercise?Why does your body do this in response to exercise?Beats per minSitting downStraight after exercise2 min after exercise
6 Anaerobic respiration Instead of glucose forming CO2 and H2O, it is broken down without oxygen into an intermediate, lactic acid, giving less energy:120 kJGlucose Lactic acid energyBUT lactic acid accumulates in the muscles causing muscle fatigue and cramps.To avoid damage to cells it has to be broken down fully to CO2 and H2O immediately after the exercise has finished. This needs more oxygen (oxygen debt)…
7 Oxygen debtIn order to get the extra oxygen to 'pay back' the debt, the body continues to breathe deeply for some time after vigorous activity has ceased.When all the lactic acid in the muscles is broken down the oxygen debt has been repaid and normal aerobic respiration resumes.Recovery time is the time taken to return to normal levels of pulse rate, breathing rate and lactic acid.It can be used as an indication of physical fitness because a fit person will recover faster than an unfit person- their breathing and pulse will return to normal in a shorter time.
8 How does training help?With exercise the pulse rate, breathing rate and lactic acid level rise less in an athlete than in an untrained personbecause training and fitness makes aerobic respiration more efficient by:improving the efficiency of the lungs and circulation.This means less of an oxygen debt is built up during exercise.Hence, less extra oxygen is needed afterwards to break down the lactic acid.
9 Only elite athletes reach top 3 Recovery timeRecovery time is the time taken to return to normal levels of pulse rate, breathing rate and lactic acid.It can be used as an indication of physical fitness because a fit person will recover faster than an unfit person- their breathing and pulse will return to normal in a shorter time.Bleep testOnly elite athletes reach top 3
10 Training summary Heart volume Volume blood pumped Resting pulse rate Explain the relationship between the effects of training & recovery time.Fitter person has faster recovery because:Improved circulation to musclesLung volumeVolume oxygen per breath Breathing rate