Final answer:
A pregnant woman should avoid deadlifts as they pose a risk of back strain from the shifted center of gravity and increased ligament flexibility. Back strain is common in pregnancy due to posture alterations and extra weight. The carpenter's trick with pliers distributes the force and prevents nails from bending.
Step-by-step explanation:
A pregnant woman should generally avoid resistance exercises that put excessive strain on her back and core or involve lying flat on her back after the first trimester. Among the options given, deadlifts are the exercise that she should avoid. Deadlifts involve a risk of straining the back, especially as the pregnancy progresses and the center of gravity shifts, which can lead to an increased risk of injury. Additionally, during later stages of pregnancy, the hormone relaxin increases the flexibility of ligaments, further increasing the risk of strain when performing exercises that require significant core stability like deadlifts.
Pregnant women often suffer from back strain late in their pregnancy because the growing uterus shifts the center of gravity, altering the posture and putting strain on the lower back. Moreover, the added weight of the baby means the back muscles must work harder to support this weight, leading to fatigue and potential strain.
Regarding the carpenter's trick, gripping the center of a nail with pliers helps because it stabilizes the nail, preventing it from bending. The pliers provide an additional point of resistance which helps absorb some of the force that would otherwise cause the nail to bend when hammered into hard materials. This principle is related to the physics of force distribution and material strength.