Exercising before a nap benefits memory better than napping or exercising alone

Sleep leads to the enhancement of memory, and physical exercise also improves memory along with beneficial effects on sleep quality. Potentially, sleep and exercise may operate independently upon memory; alternatively, they may operate synergistically to boost memory above and beyond exercise or sleep alone. We tested this hypothesis in 115 young healthy adults (23 +/- 3.9 years) randomly allocated to one of the four conditions in a 2 (exercise vs. no exercise) x 2 (nap vs. no nap) design. The exercise intervention consisted of a 40-minute, moderate intensity cycling, while the no exercise condition was an equivalent period of rest. This was followed by a learning session in which participants memorized a set of 45 neutral pictures for a later test. Subsequently, participants were exposed to either a 60-minute sleep period (nap) or an equivalent time of resting wakefulness, followed by a visual recognition test. We found a significant interaction between the effects of exercise and nap (p = 0.014, eta(2)(P) = 0.053), without significant main effects of exercise or nap conditions. Participants who experienced both exercise plus nap were significantly more accurate (83.8 +/- 2.9) than those who only napped (81.1 +/- 5.4, p = 0.027) and those who only exercised (78.6 +/- 10.3, p = 0.012). Within the combined nap plus exercise group, higher recognition accuracies were associated with higher sleep spindle densities (r = 0.46, p = 0.015). Our results demonstrate that short-term exercise and a nap improve recognition memory over a nap or exercise alone. Exercise and sleep are not independent factors operating separately upon memory but work together to enhance long-term memory.