(a) In case of temporary partial disability resulting in decrease of earning capacity the compensation shall be 80 percent of the difference between the injured employee's spendable weekly wages before the injury and the wage-earning capacity of the employee after the injury in the same or another employment, to be paid during the continuance of the disability, but not to be paid for more than five years. Temporary partial disability benefits may not be paid for a period of disability occurring after the date of medical stability.
(b) The wage-earning capacity of an injured employee is determined by the actual spendable weekly wage of the employee if the actual spendable weekly wage fairly and reasonably represents the wage-earning capacity of the employee. The board may, in the interest of justice, fix the wage-earning capacity that is reasonable, having due regard to the nature of the injury, the degree of physical impairment, the usual employment, and other factors or circumstances in the case that may affect the capacity of the employee to earn wages in a disabled condition, including the effect of disability as it may naturally extend into the future.