If a pregnant woman has to carry heavy luggage around her entire trip, she's putting herself at risk of straining her muscles, and putting undo stress on the baby. (babygaga.com)
Keep the air inside your lungs and at the same time impose a pressure on your lungs by straining your muscles. (fullhealthsecrets.com)
Also, remember when switching to heavier weights, to start out slow with one set of 6 to 8 reps to avoid straining your muscles. (reversediabetescoach.com)