After exercise, some individuals experience a pleasant feeling known as ‘runner’s high’ due to the production of endorphins - Scottish Highers Human Biology - Question 13 - 2023

To calculate the percentage increase in lactate concentration:

1. Identify the lactate concentrations at 50% and 100% exercise intensity.
   • At 50% intensity, lactate concentration is approximately 3 mmol/L.
   • At 100% intensity, lactate concentration is approximately 9 mmol/L.
2. Use the formula for percentage increase: ext{Percentage Increase} = rac{ ext{Final Value} - ext{Initial Value}}{ ext{Initial Value}} imes 100 Thus, the calculation is: rac{9 - 3}{3} imes 100 = 200\%

As the intensity of exercise increases, the muscles require more energy which leads to higher rates of anaerobic respiration due to insufficient oxygen. This process results in the conversion of pyruvate into lactate instead of being fully oxidized in the mitochondria, thereby increasing lactate levels in the blood.

One activity that may increase endorphin levels is laughter.

The endorphin concentrations after 30 minutes and 90 minutes for the unfit individual are 112 and 160, respectively. The ratio is: $112:160,$ which simplifies to $7:10.$

One other conclusion that can be drawn from this investigation is that fitness levels have no effect on endorphin concentrations after varying durations of exercise.