Developing speed is ideal for time-pressed runners because getting faster requires short, targeted efforts.
"Quick bursts improve your ability to produce energy without using oxygen, while strengthening muscles - both of which help improve your speed," says Jason Karp, an online running coach in San Diego, US (runcoachjason.com).
If you're new to speedwork or coming back after injury, reduce the number of intervals in the following workouts by half and spend more time warming up, recovering and cooling down. Add an interval every other week until you're up to speed.
You need to know your 5K and 10K race paces to do many of the workouts on the following pages. To gauge them, run one mile fast at an even pace. Note the time. To get your 5K race pace, add 40-55 seconds. For your 10K pace, add 1:00-1:15 minutes.
You've got...20 minutes
You should: Run short sprints
"It's the best workout in terms of getting bang for your buck," says Karp. "Sprints will help to improve your neuromuscular ability to produce force and power, which can improve your running economy and help delay muscle fatigue."
Run 100m all out then walk for three minutes until you have recovered and caught your breath. Repeat three times. Start and end the workout with a five-minute jog.
You've got...30 minutes
You should: Do one-minute repeats
When you run faster, "your stride length increases, and your stride turnover and arm-pumping motions change", says Karp. "Running these high-intensity repeats teaches your body how to maintain good form and how to run smoothly, quickly and efficiently."
Run one minute as fast as you can then jog for two minutes. Repeat seven times. Warm up for five minutes and cool down for four minutes.
You've got...45 minutes
You should: Run half-mile repeats
"Longer repeats increase muscle-fibre recruitment, which in turn enhances force production and delays fatigue," says Karp. "It also improves your heart's ability to pump blood and oxygen to your muscles."
Alternate fast and slow running for 35 minutes, alternate three minutes of running 15 seconds per mile faster than 5K pace with three minutes' slow jogging. Warm up and cool down for four minutes each.
You've got...An hour (or more)
You should: Do a tempo run
"Regularly incorporating tempo runs into your training will increase your aerobic capacity, allowing you to run at a faster pace for longer," says Karp. And when fatigue sets in, "you'll have the reserves to power through it".
Run at 30 seconds per mile slower than 5K race pace. Hold this pace for a 40-minute run. Warm up and cool down for 10 minutes each.
When to work an event into your schedule
Just because you're short on training time doesn't mean you can't toe a starting line. "Races are barometers of fitness," says Susan Paul, programme director for Track Shack's Fitness Club in Orlando, US. "They help you assess your strengths and weaknesses so you can adjust your training appropriately." Here's how long it takes to work up to various race distances, according to the time you can commit to training.
Running 2 days a week: 10 weeks
Running 3 days a week: 8 weeks
Running 4 days a week: 7 weeks
Running 5+ days a week: 6 weeks
Running 2 days a week: 12 weeks
Running 3 days a week: 10 weeks
Running 4 days a week: 9 weeks
Running 5+ days a week: 8 weeks
Running 2 days a week: 18 weeks
Running 3 days a week: 16 weeks
Running 4 days a week: 14 weeks
Running 5+ days a week: 12 weeks
Running 2 days a week: Not advisable
Running 3 days a week: 22 weeks
Running 4 days a week: 18 weeks
Running 5+ days a week: 16 weeks