Cause of Stiffness in Rigor Mortis

Stiffness during rigor mortis is mainly due to the formation of:

Correct Answer: Acto-myosin bond

Rigor mortis (post-mortem stiffness) is mainly due to the formation of acto-myosin bonds between actin and myosin filaments after death.

Mechanism of Rigor Mortis

1. After death, ATP production stops (no oxygen for respiration).
2. Residual ATP is depleted.
3. Without ATP, the actin-myosin cross-bridges cannot detach → permanent acto-myosin bond formed.
4. This causes irreversible muscle contraction = stiffness of rigor mortis.

Organ Most Quickly Affected by Rigor Mortis

• The Heart is the first organ to enter rigor mortis, usually within one hour of slaughter, because it uses ATP most rapidly.

Rigor Mortis Stages

• Pre-rigor: Muscle still flexible; ATP present.
• Rigor: Full stiffness; acto-myosin bonds formed; pH falls to ~5.5–5.7.
• Resolution of rigor: Autolytic enzymes (cathepsins) break down muscle proteins → meat becomes tender.