It appears that the bridge exercise has been gaining in popularity in the last five to 10 years. This is both good and bad to see especially when it is recommended for all level athletes.
The bridge is a good exercise many for beginners for strengthening of the lower back (erector spinae) muscles as well as the glutes and hamstrings. For well-trained or high-level athletes it is a waste of time, unless they are recovering from an injury, especially to the lower back.
To make sure that everyone has the same understanding of the bridge, following is a brief description:
Lie flat on the floor with your knees bent, your feet flat on the floor and your arms alongside your body. Then raise your trunk until your body forms a straight line or preferably an arched back position between your knees and shoulders. Hold for one to two seconds in the back arched position.
Because only body weight is used in this exercise you only gain strength of the muscles if your weight creates sufficient overload. For most beginners and out of shape individuals, this resistance is ample to produce some strength gains. However, because you cannot effectively increase resistance in this exercise, the amount of strength gained is very limited.
This is why you get minimal development of the hamstrings, glutes and the lower back muscles if you go into the arched back position. Stopping when you have a straight body position will not effectively strengthen the lower back muscles.
Since this exercise is commonly used to develop the core muscles it should be obvious that it is of limited value except as stated above. Much more effective for strengthening the muscles involved would be execution of the back raise, good morning and deadlift.
For more information on execution of these latter exercises see Explosive Running or Explosive Basketball Training.