Many treadmills come with a full entertainment system. You have a sound system where you can plug an iPod or watch a show on the TV screen. While these features make the training experience a pleasant one, they can ruin your exercise.
If you are hunching the shoulders or looking down to watch a TV screen ( read a magazine or play on iPod) you can develop a bad walking posture.
Whatever you run or walk the correct posture is with the head up and eyes forward. Do not hunch the shoulders and exercise with head down. If you insist to watch TV or read while doing the workout, put the magazine or the screen at the eye level. In this way you will maintain the correct posture and still be entertained.
If you continue to exercise and maintain this incorrect posture you can develop low, neck or shoulder pain. Also you will not breathe correctly and the exercise will be harder.
People develop this incorrect posture while spending many hours in the office in front of the computer. So at least when you workout you should keep the correct position.
The time on the treadmill should be spent developing good habits and improving our health. So, when you workout remember to check your posture every 5 minutes or so.