Speedwork, such as Interval Training produces important benefits, but the risk of injury is high so caution is required. Here are a number of common mistakes, most of which I've made at one time or another.
- Too Fast Too Soon. Speedwork needs to be introduced gradually, building up from the fasted pace you're used to running to the target over a number of sessions. This is the most critical aspect of speedwork safety, and it requires you to be patient and to pay attention to any early signs of potential injury. For instance, if you find your hamstrings are tight after a speedwork session, you might be Overstriding or you might lack flexibility (see below.) Do gentle increases in pace, building up to Fartlek, then structured intervals. See Practical Interval Training for details of the progression.
- Overstriding. A common mistake with speedwork is to reach forward with your legs rather than to push behind. This causes Overstriding, which puts a lot of stress on the joints. In my early days of training, I would regularly get severe back pain after speedwork because I was overstriding.
- Flexibility. Insufficient range of motion. Running faster usually requires that your legs move through a greater range of motion. If you don't have sufficient flexibility, then you are likely to get injured when performing speedwork. However, there's a goldilocks effect with flexibility; you need just enough, as too much is just as likely to cause problems as too little. In addition, stretching can cause problems, so it's important to stretch right.
- Unrealistic Goals. Speedwork paces should either be based on your actual race performance, or based on feel. Selecting a speedwork pace based on your target race pace is more likely to result in injury.
- Using GPS. While GPS can give a good estimate of how far you've run, GPS Accuracy is not enough to tell you how fast you're running at any given moment. For that you need Pace From A Footpod. In addition, small errors in distance measurement can cause serious problems when doing speedwork. I would recommend using a track, or carefully measuring the distance between convenient markers.
- Hard Braking. At the end of a high speed interval you need to slow up in a controlled manner. Slowing up too hard, or letting your biomechanics fall apart can lead to injuries. You should never hear your feet slap, and you must keep your Running Form normal until your speed has dropped to the point you can transition to walking pace without slowing up further.
- Sudden Stops. Coming to a complete stop during the rest periods of interval training can cause a drop in blood pressure and even trigger fainting. (This is probably because the calf muscle helps pump blood.) Try to keep moving after the interval; this should also help keep your intensity up, as counterintuitively it will improve your recovery.
- Slipping. If your feet slip, your leg will move more rapidly and further behind you than normal and can put extra strain on your hip flexors. Obviously a more dramatic slip can cause a fall. Avoid speedwork in icy conditions, and use running shoes that have a high grip. (Some shoes have plastic nubs that give outstanding grip on asphalt, even when it's wet.)
- Treadmill. A treadmill can be used for some types of speedwork, and it has the advantage of keeping you on pace. However, most treadmills don't accelerate or decelerate between dramatically different paces, making the transition difficult. I would urge caution to avoid making an error and falling off the treadmill; that could result in a dramatic injury.
It's worth considering doing some interval training, especially High Intensity Interval Training on a stationary bike rather than running to reduce the risk of injury. Always remember Golden Rule of Training The primary goal of training is to stay injury free so you can continue training