A. Fast muscle fibres ii. Lactic acid

The lactic acid is produced in the fast muscle fibres due to the larger exercise-induced loss of K⁺ ions as compared to slow muscle fibres.

B. Slow muscle fibres i. Myoglobin

Slow muscles fibres have a higher rate of myoglobin concentration as compared to the fast muscle fibres.

C. Actin filament iv. I-band

The I-band contains only thin (Actin) filaments in the myofilament.

D. Sarcomere iii. Contractile unit

A sarcomere is the functional contractile unit of a muscle fibre which contains two types of myofilaments myosin and actin.