There's a much higher incidence of injury doing flat sprints vs. hill sprints. On a steep hill you can't really get going that fast, but you're exerting yourself to the same extent. Since the goal is the exertion, not the speed, it's a much better choice.

I can't imagine that sprints will hurt you. Just warm up well and ease into it. So, don't go out and kill yourself the first day. Go at 60% and then build up over time. Admittedly this is not my area of expertise, but after 15 years of inactivity I started doing Crossfit, which included a lot of sprints. I scaled... eased into it, and had no injuries.

I was doing 400m sprints yesterday and pulled a hamstring.

Nevertheless, I'm a huge advocate of them. 400m sprints, 100% effort, with a 3-minute walking rest between sprints. 8 of them.

Put in 100% and you'll get amazing results. Possibly as tough as it gets workout-wise but tremendous upside.

some good ideas here: http://paleohacks.com/questions/693/sprint-intervals-most-effective-techniques#axzz1Gy5lxV2g

Just ease into the sprints. Make sure recovery is good. And you can do swim sprints, or on a stationary bike.

I like uphill sprints, but for that you need a hill...

Btw, 30 minutes of abdominal exercises???

If you have a history of fluoroquinolone antibiotic use, corticosteroid use (especially injections to that area), past history of Achilles tendon injuries, then, yes, you probably want to see a physician before embarking on heavy sprints. Otherwise, what Sara said--ease into it. The biggest risk factor, besides those specific medications and age is going beyond your range of motion and going too heavy right off the bat. Work on your ankle mobility, go easy and you should be fine.

Keep in mind too, you can "sprint" on the elliptical machine, the rower, etc. I find those to be low-impact alternatives.

The fitter and stronger you are the faster you can sprint, and the faster you can sprint the more likely you will get injury. Runners-sprinters often have muscle pull injuries in hamstrings and achilles tendons. They generate so much force, and achieve so high speed that overloads muscles (sprinters usually have huge!!! legs) and may pull or tear them. Make sure you strengthen you hamstrings with dead lifts, and/or kettlebell swings.

I try to always do my sprints on grass.

I do them in some sort of minimalist shoe. Warm up. Start slow. Ease into it. Then go flat out! Anything is better than nothing!

If you want to mitigate injury, and you don't already own a pair, consider getting a pair of minimalist footwear like Vibram Fivefingers. If you're going to slowly ramp up your sprints over the course of a couple weeks, this would be the perfect time to adapt to such shoes. As your muscles develop, you'll get a better workout and take stress off other areas of your feet/legs.

If you are healthy and have no injuries then there is no reason not to sprint. Sprinting doesn't give you injuries! Running/Sprinting with bad technique gives you injuries. Only efficient, well coordinated movement is healthy.

Assess and correct movement patterns. Physiotherapist Gray Cook: http://www.youtube.com/watch?v=75-c_xYHZHQ

Coach John Siffermann:

http://physicalliving.com/natural-movem ... n-perfect/

Most people are far from optimal in their movement patterns (result of too much sitting). Look for a Functional Movement Test (Gray Cook) or even better: Selective Functional Movement Assessment (SFMA) . I did the FMS test some month ago. It is cheap and easy to do.

http://www.functionalmovement.com/SITE/

Another cause of injury besides bad coordination is overdoing it. Your tendons, ligaments and connective tissue in general have to adapt to the increased demand and this will take some time. More time than for muscles

http://www.exerciseology.me/doug_kelseys_blog/2009/03/healing-and-strengthening-tendon.html

So ease into it. But this is also true for weightlifting, climbing, martial arts or whatever movement you do. If your training load exceeds your current capacity you are at risk.

Ageism is bad for your health. All self-limiting belief systems are. So get rid of it. Don't think you are crap just because you are over 40 or 50. You are crap because of 30 years of unhealthy lifestyle.

74 year old Ernestine Shepherd has no injuries (5ks, 10 ks, Marathons, weightlifting). She started training at the age of 56.

http://www.youtube.com/watch?v=0OR-6y-8-nM

Madonna Buder did the Hawaii Ironman at 77. She started training in her mid forties. http://www.youtube.com/watch?v=nUp9v8A46dk

I have no probs with sprints. But I watch my technique, use barefoot shoes and started to learn POSE Running. I strongly recomment using a POSE Running Coach if you have problems with running or sprinting.

http://runningengineer.com/human-movement/

http://runningengineer.com/pose-method/

For warm up I strongly recommend Joint Mobility (no - not stretching) I do it as a warm up with my dance students . It helps to transform motor morons into better movers. Your muscles do exactly what your brain tells them to do. You have to talk with your nervous system, not with your muscles.

What is Joint Mobility? Coach John Siffermann explains:

http://physicalliving.com/tuesday-qa-wh ... sifferman/

Interview with Sambo Coach Scott Sonnon about joint rehab (he had severe joint problems as a young man).

http://physicalliving.com/exclusive-int ... ng-system/

Injuries can happen with any exercise. Sprint in the grass. Walk/Jog your sprint "lane" before you sprint to check for dips in the grass or objects that can cause a injury.

Will pipe in here because I did not begin working out regularly until age 40, and I do have Achilles tendon issues (was far from sedentary before that though). If you have pain at all there I'd recommend getting X-ray'ed at a podiatrist: ended up having small bone spurs/calcification at the rear of my healbones.

As others have said, ease into it. I did 15 to 20 minutes on an elliptical, couple times a week at 80-85% of maximum heart rate. After a year of this I underwent the dye injected stress test - all clear so then comfortable going to interval training. Still primarily used the elliptical but after reading Cordain, Sisson and others I moved to sprints.

A key item is to warm up first, then stretch the Achilles out. I typically do a slow jog, or medium resistance on elliptical for about 3 minutes to get blood flowing to the muscles. Then I spend a few minutes doing lunges, holding for about 30 seconds, back leg straight front leg bent, back heal down firmly on the floor. Hold for 30 seconds so that things really stretch out. This is sometimes followed by stretching of the quads and hamstrings, but not always.

After that I typically run flat out till heart rate reaches 90-95%, hold for one minute. Slow jog or fast walk for 3 or 4 minutes to cool off/rest, then repeat the cycle; number of sprints of three or so. Stretch Achilles afterwords.

Now in my m mid-40s I can report no Achilles tendon or other injuries, and my time to sprint/jog/sprint/walk/sprint a mile has been reduced by a full minute, this year alone. Have reduced this exercise to once a week as Grok might have. Doing so seems to continue to help raise my IGF-1 levels.

Recently I've started to do jog/sprint intervals over by the east river on the Lower East Side, and I have to say I love it! I'll do an easy jog from my apartment over to the water, walk and stretch, then start up.

Yesterday I did about 6 sprinting sections of about 30-40 seconds each, all out, with a jog in between for active recovery. I also did 3 sets of box jumps, 1 on benches that were about 16" high (knee height), on to the top of a picnic table about 28" high (waist height?) and then from the seat of the table, to the table top, back down with a 180 at the top and bottom. I feel great, and slept like a baby, but I am SORE today! Don't know if it's from the sprinting or the box jumps, but my inner thighs, groin and glutes are really tight and sore.

I use conventional Nikes, but I've been lusting after the New Balance Minimus Trail shoes.