Thigh muscles get tired but not the muscles of the ventricle of heart because

The time period between the beginning of the electrical response and the peak of tension recorded is known as:

Rahul exercises regularly by visiting a gymnasium. Of late,he is gaining weight. What could be the reason? Choose the correct answer and elaborate.
$A$. Rahul has gained weight due to accumulation of fats in the body.
$B$. Rahul has gained weight due to increased muscle mass and loss of fat.
$C$. Rahul has gained weight because his muscle shape has improved.
$D$. Rahul has gained weight because he is accumulating water in the body.

Which of the following statements are correct regarding skeletal muscle?
$A$. Muscle bundles are held together by a collagenous connective tissue layer called fascicle.
$B$. Sarcoplasmic reticulum of muscle fibre is a storehouse of calcium ions.
$C$. Striated appearance of skeletal muscle fibre is due to the distribution pattern of actin and myosin proteins.
$D$. $M$ line is considered as the functional unit of contraction called sarcomere.
Choose the most appropriate answer from the options given below:

Select the correct statements regarding the mechanism of muscle contraction.
$A.$ It is initiated by a signal sent by $\text{CNS}$ via a motor neuron,not a sensory neuron.
$B.$ Neurotransmitter generates an action potential in the sarcolemma.
$C.$ Increased $Ca^{++}$ level leads to the binding of calcium with troponin on actin filaments.
$D.$ Masking of the active site of actin prevents contraction; unmasking leads to contraction.
$E.$ Utilising the energy from $\text{ATP}$ hydrolysis to form a cross-bridge.

According to the sliding filament theory: