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

Input:
Question: Does anyone use the SpeedSac on a track surface? If so, how durable is the rubber? My plan is to buy 3 or 4 and use them for the younger sprinters.
Document: The bag itself is heavy duty rubber, which glides nicely over a variety of surfaces. I even used it on concrete to test the durability. It survived without visible damage, but I suspect that such an abrasive surface will shorten its lifespan, so I use this primarily on a grass field. It would, however, also be quite useable on a nicer track surface, something other than dirt.
I am a mid-distance runner ranging form 400m-800m and needed some speed to take out of the blocks and maintain. The speedSac is a very useful piece of equipment that will build strength and speed. I used it summer 2012 and drooped from a 6.12 in the 40 yard dash to 4.9 training with my teammates. I recommend this for athletes or anyone that isn't afraid of a hard workout. This will bring the beast out of you. Very durable sac.
This is not just for the sprinter. Anyone who needs to build strength and staminacan use this for their regiment.You can vary the resistance from 1-30 lbs by filling 3 bags with sand.The strap is comfortable and adjustable.It's more stylish than the truck tire tied around the waist, but may be scratched ifused on street / concrete pavements.Helpful DVD how to maximize results.And, why buy the sand when you can just get it from the beach?
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.
As a household with a 4 sport athlete this product is awesome to have for personal training. It comes with a DVD that has a 6 week training program created buy professional trainers. We have lots of SKLZ products and have never been disappointed. They are durable, very helpful and most (the ones we own) are for general workouts, speed, strength, jump height, agility, but they also make items for specific sports to help increase your abilities in that sport !!
It fits really well on myself and my older sons. It is a bit loose on my 7 and 9 year old sons, but they are still able to use it. The sled portion that holds the sand bags is a thick rubber mat. As long as you use it on soft grass and not a hard surface like concrete, gravel, or a driveway, it should last you a very long time.
The SKLZ SpeedSac is a great tool for building explosive speed. The soccer team I coach developed first step quickness using the speedsac. It's also a great workout tool for anyone wanting to get in shape. The reason for the 4 stars is the belt was way too big for my 9 and 10 year old girls team. I would be great if they offered a smaller belt. I would recommend this for any athlete wanting an explosive first step.
I purchased two SpeedSac for training a high school basketball and volleyball teams. Both teams have used and the players really enjoyed working out with the SpeedSac. The SpeedSac is mainly used indoors for now and worked out great. The players found it easy to change out the weight bags according the weight they needed to pull.The construction of the SpeedSac appears to be very durable and portable with interior handles. The SpeedSac exterior has a good rubber covering that did not scratch the gym floor.
However, when I do use it, sprinting with the SpeedSac leaves utterly tired, sweaty, and feeling good for having worked myself so hard.I am giving it 4 stars because sand tends to trickle out of the yellow bags. Maybe I'm not sealing them correctly. The sand gets trapped in the velcro and endes up in the big black bag. A minor annoyance.
This product is great. I use it every week in my training and I can honestly say that it's one of the things that's allowed me to see the most improvements in my sprinting the fastest. The best thing about it is that it's portable and durable. For people like me that train alone most of the time, it's the perfect accessory because you can use it all by yourself. It comes with 3 bags, but I think you could squeeze up to 5 in there if need be.
Answer: yes