Muscle fatigue occurs due to the accumulation of

1.  $C{O}_2$

2.  Myosin ATPase

3.  Lactic acid

4.  Creatine phosphate 

The muscle can directly use which of the following as a source of energy?
1. Creatine phosphate
2. Glucose
3. ATP
4. Fatty acids

Repeated activation of the muscles can lead to

1. Accumulation of pyruvate due to anaerobic breakdown of glycogen

2. Accumulation of lactic acid due to anaerobic breakdown of glycogen

3. Fatigue

4. Both 2 and 3