I believe that is true both physically and spiritually. My own laziness has caused much harm, both physically and spiritually.
Proverbs 21:25: The desire of the slothful killeth him; for his hands refuse to labour.
Lazy individuals do not get as much exercise as the industrious. Workers get stronger and idlers get weaker. Medically speaking, idlers plug up their arteries, which causes weakness, heart attacks and strokes. Our physical hearts are muscles. They need exercise in order to be strong.
1 Timothy 4:8: For bodily exercise profiteth little: but godliness is profitable unto all things, having promise of the life that now is, and of that which is to come.
Physical exercise profiteth little. Spiritual exercise profits more. Our spiritual hearts also need exercise. We NEED to do what the Lord wants us to do. We NEED to serve Him. Spiritual exercise does more good than physical exercise and spiritual laziness does more harm than physical laziness.
Acts 24:16: And herein do I exercise myself, to have always a conscience void of offence toward God, and toward men.
1 Timothy 4:7: But refuse profane and old wives* fables, and exercise thyself rather unto godliness.