Instruction: Output yes if the supporting document can answer the given question. Otherwise, output no.

Input:
Question: Any reason why I can't use weights instead of sand? I want to adjust total weight and weights would be easier than dumping / filling sand.
Document: As for the weight bags, they were easy to fill with sand and close up with two velcro sealing sections. The weight bags when sealed left small openings. The openings allowed for a small amount of sand to leak out when we used them as weights for lunges. I would have given the SpeedSac 5 stars if not for the small leak from the weight bags.
This portable sprint start sled works well. Filling the 3 sacks with sand from a long-jump pit provides the 30 pounds of weight that the sprinter drags to developing starting power. The sand is then dumped back into the long-jump pit after the workout. It would be much less practical to have to haul the thirty pounds to the track. I have also put 2 25-pound barbell plates into the bag and been able to drag 50 pounds in an indoor starting practice session. This worked fine.
This trainer is a high quality piece of equipment. It is very simple to use, and only requires filling the bags with sand to get started. Sand is not included, but you can get that cheaply locally.I have used this trainer a few times with my sons. You can really feel a difference when you run while dragging the weight.
As a track coach, this is a great tool for building up sprinters and runners early on in the season. I like the variability of weights and it is clearly a durable product. The big disadvantage for me is that you can't really use it on the track itself because it'd get torn up. So you're stuck with on grass or in the gym. Which is okay because you're not going to run long distances with this, and there are other products designed to work with starting blocks.
My son is a football lineman and we've tried parachute speed trainers and breakaway straps. The SpeedSac is easy to use, with sturdy weight bags that you fill with sand or, if you're ambitious, lead shot. It works best on grass since the friction won't prematurely wear out the large weight container. This is the best resistance speed training system that we've tried and it's reasonably priced. I think it would fit a wide range of people. My son is 6-1 and 250.
Works well for a wide age range. Easy to use and durable. Easy to adjust weight. Easy to transport with one hand. Great product.
This is a very nice set of exercise equipment that will help you exercise your leg muscles. After 20 minutes exercising you will discover muscles that you never new were there, as they all will be hurting like hell.The sealing of the packages is excellent, so you do not make a mess after filling the bags with sand. I use my bags in my basement and there is no sign of sand anywhere.
As it is with any sports training aid, it isn't going to do the work for you. You have to get out there and run the sprints, and move laterally and then run backwards. You have to push yourself and run hard. If you do, then this sprint trainer is great. It straps easily around your waist, and has 3 ten pound sand bags so you can adjust the weight. Just don't expect easy results. You must still work hard.
High quality construction from SKLZ again with this sprint/speed trainer. The only drawback is you have to have your own sand be it digging around somewhere or store bought clean stuff, your call.Like many speed trainers, this device works on exploding off the mark hence you shouldn't need all that much weight. This is to adjust your body to the additional mass/weight, so that when you don't have them, you should accelerate off themark much quicker.
I bought it for my daughters who are very involved in soccer. I was wanting something to increase their speed, did some research and found the SpeedSac. The reason I bought this instead of one of the other products out there was first the cost, and secondly the ease of using it.
Answer: yes