Will using the treadmill with ankle weights make my workout more effective?

Adding weight to your body such as ankle weights or weighted vests can help increase the work your body is doing. If you are trying to increase leg strength or burn additional calories, this is a good way to get more out of the time you spend on the treadmill. This additional  weight will cause your body to generate more power to stay at the same speed or incline you had when you were not using it. This additional power will equal an increase in the calories burned and strengthen your legs, provided that your do the same workload (speed and incline) as you did without additional weight. If you have to reduce the workload, then the off-set of the weights might not be worth it. Adding weight should only be done if you have achieved a good fitness base and your form on the treadmill is good. One concern is the weight might change your gait or posture. If you don't have good core strength, leg strength, or proper walking/running form, then the added weights will just put more stress on your weak muscles and an overuse injury could occur.