Effects of outdoor walking and infant carrying on behavioral and adrenocortical outcomes in mothers and infants

Research in school-aged children demonstrates positive effects of outdoor walking on behavioral self-regulation. Furthermore, studies report stress-reducing effects of proximity on infants and mothers. To date, no studies have assessed the effects of an outdoor walk as well as infant carrying on infants and their mothers in the postnatal phase. This study assessed the effects of a 30-min walk in an outdoor green environment (vs. staying indoors) and proximity through infant carrying (vs. using a pram) on infants and their mothers. Effects on infant cortisol and sleep, maternal cortisol and mood, and mother-infant adrenocortical synchrony were examined. Infants (N = 101, 0–5 months old) were exposed to a mild naturalistic stressor. Mother-infant dyads were subsequently randomized to one of four conditions: walking in an outdoor green environment with the infant in a pram or a chest carrier, or staying indoors with the infant in a pram or a chest carrier. Mothers reported infant's sleep in minutes after the conditions, and maternal mood through visual analogue vigor and affect scales both immediately before and after the conditions. Cortisol concentrations of mother and infant were determined through five saliva samples throughout the experiment. After the stressor, carried infants showed a greater decrease in cortisol values compared to infants in the pram, regardless of whether they were walked outdoors or stayed indoors. Infants who were walked outdoors in a carrier or pram slept longer than infants who stayed indoors in a pram. In contrast, mothers staying indoors showed a greater decrease in cortisol concentrations as compared to mothers walking outdoors. Compared to mothers having their infant in a pram, mothers who carried their infant showed a greater decrease in cortisol concentrations. Indoors, maternal vigor decreased from the pre-to post-condition, while mothers going outdoors showed no decrease. There was no difference in maternal affect or mother-infant adrenocortical synchrony between conditions. Our findings have implications for caregiving advice, as well as for future research on the stress-reducing potential of the outdoors in combination with infant carrying.