•Families, peers, and health care providers are important sources of interpersonal influence that can increase or decrease commitment to and engagement in health-promoting behavior.•Situational influences in the external environment can increase or decrease commitment to or participation in health-promoting behavior.•The greater the commitments to a specific plan of action, the more likely health-promoting behaviors are to be maintained over time.•Commitment to a plan of action is less likely to result in the desired behavior when competing demands over which persons have little control require immediate attention.