Recently, administration of nicotinic acid (NA) at a pharmacological dose was found to induce a similar change in the muscle´s contractile and metabolic phenotype as observed in response to endurance exercise. Thus, the hypothesis was tested that combined NA administration and endurance exercise promotes the adaptation of muscle to regular exercise and improves the endurance performance to a greater extent than exercise alone. Thus, 30 adult mice were randomly divided into three groups of 10 mice/group. The control and the exercise (EX) group received an adequate NA diet, while the EX + NA group received a high NA diet. Mice of the EX and the EX + NA group were subjected to a treadmill endurance exercise program five times/week during the experimental period of 42 days. At day 41, endurance performance was greater in the EX + NA group than in the control and the EX group (p < 0.05). Mice of the EX + NA group had a higher type IIA (+60%) and a lower type IIB (−55%) fiber percentage in gastrocnemius (GN) muscle than control mice (p < 0.05), while the type I fiber percentage in GN muscle tended to be increased (+100%) in the EX + NA group compared to the control group (p = 0.051). In the EX + NA group, glycogen concentration (+15%) and mRNA levels of two glycolytic (+70–80%) and two glycogenolytic enzymes (+80–120%) in GN muscle were increased compared to the control group (p < 0.05). In conclusion, feeding a high NA diet induces changes in skeletal muscle fiber composition and improves endurance performance of mice subjected to regular endurance exercise.