Which type of workout is going to produce better results, tempo training or intervals? According to research done by Peter Snell (Olympic sprinter of 1960 and 1964) at the University of Texas Southwestern Human Performance Center, priority should be given to interval training. His research consisted of comparing performance gains between two control groups of runners, one of which did tempo training twice a week and one group that did interval training.

[...] the interval-trained runners gained considerably more physiological and competitive fitness. A key lesson to be learned here is that intensity is always the most-potent producer of fitness; it is a much-stronger stimulus for improvement than training volume and workout frequency. When you conduct your intervals at 90 to 100 percent of VO2max (and at higher intensities, too), the amount of fitness gained per minute will always be greater, compared with the running capacity accrued at lower intensities. As you can see from Snell’s research, each minute of high-quality work can sometimes produce twice as much gain in fitness as double the amount of lower-quality exertion.

For myself, I strive for a good mix. When I am building an aerobic base towards the beginning of a season or after a marathon, I tend to stick to tempo training and easy runs. When I am aiming to peak for a specific race and to get into top-shape, I will mix interval and fartlek work in as well. It seems to work out fairly well. The priority certainly goes to the interval training, but tempo runs are easier to fit in. This is especially true at this time of year when it can be dark and the footing is less than favorable at the times that I run.

(Sources: Tom Ryan – Run Coach – Running Research News)