When you have a pain in the neck -- literally -- it could be caused by tension. Tension can set off a chain of events that leads to soreness at trigger points, which sometimes feels like knots in a muscle.

Physical exhaustion develops as a normal response to overexertion or not adequately resting between periods of physical activity. No matter the cause, physical exhaustion is a serious condition that should not be overlooked. Rest and recovery help you recover from exhaustion.

Your lumbar and sacral vertebrae are part of your lower back region. You have five lumbar vertebrae and five sacral vertebrae, the latter of which are fused together to form the sacrum. The two areas meet at the L5 and S1 vertebrae. This part of your spine can become stiff with age and lack of use.

Muscle pain, muscle weakness and paralysis can be signs of serious muscular problems. MedlinePlus says that muscle disorders can occur as a result of injury, overuse, infections, medications, genetics and inflammation. Muscular system diseases require various forms of treatment approaches.

Your spine has 24 bones called vertebrae that are stacked on top of one another. If one of these bones cracks or collapses due to pressure or an injury or a disease like osteoporosis, it is called a spinal compression fracture.

The human muscular system includes skeletal, smooth and cardiac muscle tissue. Skeletal muscles attach to your bones, stabilizing the skeleton and enabling voluntary and reflexive movement. Smooth muscle tissue found in blood vessels and various body organs produces involuntary movement essential for normal function.

Creatine phosphokinase, or CPK, is an enzyme that is present in the heart, brain and skeletal muscles. CPK is more commonly known as creatine kinase, or CK. CK is released from the cells of these tissues when they are injured or do not receive enough oxygen.