 Energy is needed in three(3) places › At the cross-bridges for movement  Sliding Filament Mechanism › At the cross-bridge & Actin binding site  To break connection › At the Sarcoplasmic Reticulum  To pump Ca+ back into the S.R.

 ATP › Best source of energy › Only last about 3-5 seconds on the body and is used even faster.  Creatine Phosphate › 4  6 times more abundant in the body than ATP. › Is broken down to make ATP. › Can provide enough energy to sustain muscle contraction for about 15 seconds.

 Glycogen › Stored form of Glucose (sugar) › Is broken down to make ATP. › Can provide enough energy to sustain muscle contraction for several mins.  Fat › The body will turn to fat as a source of energy for muscle contraction when the contraction is for a prolonged strenuous activity and when the other sources of energy have been used up.

 Oxygen is required for cells to make ATP. › Cellular Respiration: process that makes ATP. › Fermentation: process that makes ATP without oxygen.  Oxygen Debt: If the cells doesn’t have enough oxygen carry out respiration it shifts to fermentation. › Lactic Acid is a by-product of fermentation and can build up in the cell, it also requires oxygen to be broken down. › Heavy Breathing, Muscle Cramps, Muscle Spasms › Muscle Fatigue: The inability for a muscle to contract in a normal manner.