Whether you are a lawyer, a soccer mom or dad, or a professional runner, we all want to make the best use of our training time. Although it may take around 100 miles of running per week to reach your full potential as a marathoner, you probably lack the time or the inclination to run that much. So, how can you make your workouts more efficient and obtain the greatest benefit in the least amount of time?

If you only have time for a few runs per week, five or six miles at an intensity easy enough to let you sing along with your iPod isn't going to cut it. The fewer workouts you do, the greater the importance of each workout. Below are the most effective workouts for improving your marathon performance.

Long Runs
What: The staple of marathon training, long runs are significantly longer than any of your other daily runs. Since your body has a much better concept of time than of distance, the amount of time spent on your feet is more important than the number of miles you cover.

Why: It has been known since the 1960s that the ability to perform prolonged endurance exercise is strongly influenced by the amount of carbohydrates stored in skeletal muscles (glycogen), with fatigue coinciding with glycogen depletion. To the marathoner's benefit, the human body responds rather elegantly to situations that threaten or deplete its supply of fuel. When glycogen is depleted by running, muscles respond by synthesizing and storing more than what was previously present. Empty a full glass, and you get a refilled larger glass in its place. The more glycogen you have packed into your muscles, the greater your ability to hold your marathon pace to the finish.

In addition to serving as a stimulus to store more glycogen, long runs improve your blood vessels' oxygen-carrying capability by increasing the number of red blood cells and hemoglobin concentration. They also create a greater capillary network, providing more oxygen to your muscles, and increase mitochondrial density and the number of aerobic enzymes, increasing your aerobic metabolic capacity.

Long runs also prepare your muscles and connective tissue to handle the stress of pounding the pavement for 26 miles. For this reason, all of your long runs should be on the road (unless you're planning on running a trail marathon).

How: While you should try to not let your long run comprise more than about thirty percent of your weekly mileage, this rule can be broken in the name of necessity if you plan on running only a few times per week. Run at a comfortable, conversational pace (about two minutes per mile slower than 5K race pace, or about seventy to seventy-five percent of maximal heart rate). Lengthen your long run by one mile each week for three or four weeks before backing off for a recovery week. If you run more than about 40 miles per week, or if you run faster than about 8-minute mile pace, you can add two miles at a time to your long run. Keep adding miles until you reach 22 to 24 (or about 3 to 31/2 hours, whichever comes first), and do your longest run three weeks before your marathon. In a study I conducted on the training characteristics of the 2004 U.S. Olympic Marathon Trials qualifiers, I found that the men's and women's longest runs averaged 25 and 23.5 miles, respectively, and that they ran longer than 20 miles an average of 18 and 10 times, respectively, during the year leading up to the trials.

Lactate Threshold (LT) Runs
What: LT runs are performed at the intensity corresponding to your lactate threshold, an important physiological variable that demarcates the transition between exercise that is almost purely aerobic and exercise that includes significant oxygen-independent (anaerobic) metabolism. (All running speeds have an anaerobic contribution, although when running slower than your LT pace, that contribution is negligible.) Therefore, the LT represents the fastest speed you can sustain aerobically. From the time of the classic study published in Medicine and Science in Sports and Exercise in 1979 by some of the most prominent names in exercise physiology (Farrell, Wilmore, Coyle, Billing, and Costill), research has shown that the LT is the best physiological predictor of distance running performance.

Why: LT runs, which give you the best aerobic bang for your buck, raise your LT to a faster speed, which allows you to run faster before you fatigue because you can run faster before anaerobic metabolism begins to play a significant role. The benefit of being able to run aerobically at 5:30 pace compared to 6:00 pace is obvious. Since optimal marathon pace is only about 15 to 20 seconds per mile slower than LT pace (with the difference in paces getting larger as performance level declines), the goal of marathon training is to raise your LT and to increase your ability to sustain as high of a percentage of your LT as possible.

How: For average runners, LT pace is approximately 10 to 15 seconds per mile slower than 5K race pace (about eighty to eighty-five percent of maximal heart rate). For those more trained, it's about 25 to 30 seconds per mile slower than 5K race pace (about ninety percent of maximal heart rate). Subjectively, these runs should feel "comfortably hard."

I typically use three types of LT workouts with the marathoners I coach: 1) continuous runs at LT pace, starting at about 3 miles and increasing up to 7 to 8 miles (or about 45 to 50 minutes, whichever comes first); 2) intervals run at LT pace with short rest periods, such as 4 to 6 x 1 mile at LT pace with 1 minute rest; and 3) shorter intervals run at slightly faster than LT pace with very short rest periods, such as 2 sets of 4 x 1,000 meters at 5 to 10 seconds per mile faster than LT pace with 45 seconds rest and two minutes rest between sets.

Lactate Threshold/Long, Slow Distance (LT/LSD) Combo Runs
What: As their name implies, LT/LSD combo runs combine long, easy runs with segments at LT pace.

Why: LT/LSD combo runs let you simulate the physiological and psychological fatigue of the marathon without having to run as far. Like long runs, they severely lower muscle glycogen, stimulating its synthesis and storage.

How: Do your LT/LSD combo runs as a medium-long run (12 to 16 miles), including LT segments at the beginning, middle, and/or end of the run. Some examples are: 1) 4 miles at LT pace + 8 miles easy; 2) 5 miles easy + 3 miles at LT pace + 5 miles easy + 3 miles at LT pace; and 3) 10 miles easy + 4 miles at LT pace. After you've done a number of these runs, try running faster than LT pace for the last mile or two of the final LT segment, which will get you sharp for the marathon. For example, run 9 miles easy + 4 miles at LT pace + 1 to 2 miles faster than LT pace. You may want to run the LT segments on a track, where you can closely monitor your pace. Because these workouts are very tough, alternate the long run with the LT/LSD combo run every other week, and after three or four weeks, don't do either run for one recovery week.

Time is a valuable commodity. If you don't have the time to run 100 miles per week but still want to improve your marathon performance, try these three marathon workouts. With all of the time you'll save, you'll be able to watch your kids at soccer practice.

Jason R. Karp is a professional coach, freelance writer, and Ph.D. candidate in exercise physiology at Indiana University, currently living in Albuquerque, NM while working on his dissertation. His writing has appeared in numerous international running, fitness, and coaching magazines and scientific journals. He has coached high school and college cross country and track and field, and currently coaches athletes of all levels through RunCoachJason.com.