When he resigned, Benedict cited his advanced age as the reason, saying he no longer had the strength for "an adequate exercise of the Petrine ministry".

BBC: Ex-Pope Benedict returns to Vatican

After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry.

CNN: Full text of Pope Benedict XVI's declaration

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine Ministry, " he added.

WSJ: Pope Benedict XVI to Resign

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry, " he told the cardinals.

NPR: Pope Resigning On Feb. 28, Conclave In March

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine Ministry, " the pope said in a declaration in Latin to a gathering of cardinals on Monday.

WSJ: Pope Benedict XVI to Resign

Simply doing aerobic exercise such as walking or light treadmill workouts will not be adequate to preserve muscle tone, bone health, balance and posture.

FORBES: Why Strength Training May Help You Live Longer

Scientific evidence shows that adequate night-time sleep is just as important as healthy eating and regular exercise for children to develop.

BBC: Children losing out on sleep