What energy systems does your body use to support the 100s trial in the experiment? refer back to information presented in activity 4.4.1?

I believe at the beginning, the body used up ATP energy in the muscles to support the enduring muscle contraction activities. Once the ATP was used up, the body had to switch to lactic acid fermentation in order to get energy needed support a continued muscle contraction. Muscles need energy to produce contractions, this energy is derived from adenosine triphosphate present in muscles. Muscles tend to contain only limited amount of ATP, therefore when depleted ATP needs to be resynthesized from other sources. 

Twenty one miles per hour

You didn’t give us any choices