Long slow distance (LSD) is a form of aerobic endurance training used in sports including running, rowing, skiing  and cycling. Physiological adaptations to LSD training include improved cardiovascular function, improved thermoregulatory function, improved mitochondrial energy production, increased oxidative capacity of skeletal muscle, and increased utilization of fat for fuel. Ernst van Aaken, a German physician and coach, is generally recognized as the founder of the long slow distance method of endurance training.
Long slow distance training is a form of continuous training performed at a constant pace at low to moderate intensity over an extended distance or duration. The moderate training intensity of LSD is effective in improving endurance and maximum oxygen uptake in individuals who are undertrained or moderately trained. Although Long slow distance training is not effective when used in isolation by well-trained athletes,  there is substantial evidence that Elite athletes spend 70% percent or more of their training time at LSD output levels, that Long Slow Distance effort levels are a necessary part of the training of world class athletes, and that LSD workouts are primary drivers of the lower resting heart rates seen in well conditioned athletes.
Tim Noakes, a professor of exercise and sports science at the University of Cape Town, suggests that it was Arthur Newton who initially proposed that running longer distances at slower paces was the most effective training method for beginning runners. Noakes asserts that after this method was rediscovered in the 1960s, Joe Henderson coined the term "long slow distance".
Long slow distance running was promoted as a training method by Joe Henderson in 1969. Henderson saw his approach as providing an alternative to the dominant school of training for distance running which he called “PTA school of running – the pain, torture, and agony” approach. He documented the success of six competitive runners who followed in one form or another an LSD training regime, sometimes combining a few more strenuous workouts with the regular long slow distance running with weekly mileages ranging from 50-60 to 120–150 miles per week, with marathon personal bests between 2:14 and 2:50 hours. In addition, there are ultra-marathoners who use a similar method for training. A typical 5k runner might consider 8 to 10 miles of LSD, while a marathoner might run 20 or more miles. LSD runs are typically done at an easy pace, 1–3 minutes per mile slower than a runner's 10k pace. The objectives of these runs are to build blood volume and to increase muscle strength, endurance, and aerobic fitness.
Henderson's book was not only directed at competitive runners, but also at runners who wanted to have fun running. He writes, “LSD isn't just a training method. It's a whole way of looking at the sport. Those who employ it are saying running is fun – all running, not just the competitive part which yields rewards.” 
Approaches to running
During the running boom of the 1970s, many recreational runners used LSD as a basis for training. One of the "fathers" of the Honolulu Marathon, cardiologist Jack Scaff used a long slow distance approach to train runners in his marathon clinics. Scaff advised his runners to follow the "talk test", an idea that had originated from Arthur Lydiard in which runners should be going slow enough to be able to hold a conversation. According to sportswriter John Brant in his 2006 book Duel in the Sun, almost every serious distance runner in the early 1980s used Lydiard's system of building an endurance base with many miles at an aerobic pace before running shorter distances at an anaerobic pace.
Starting out with an hour run, three times a week, and building up to weekly averages of 40 to 60 miles a week for the last three months, thousands of graduates of the program have found that they could complete the full Honolulu Marathon which is held every year in beginning of December. The clinic's approach can be seen from its original Rules of the Road, now referred to as the "basic set of rules that lay the foundation for your training."
- The rules:
- No fewer than three runs per week
- No more than five runs per week
- No less than one hour per run
- No farther than 15 miles on any run
- One run per week lasting two hours or more (after month 5)
A variant of the LSD approach is to combine running slowly with walking breaks.
- "It has been found that average runners will have more success if they take regular walk breaks.
- "The strategy is unusual in that it doesn't involve simply walking when you are tired. Walk-break runners force themselves to stop even at the beginning of a run when they are fresh."
An example of such an approach is provided by the running clinics organized by Jeff Galloway In running circles, John Bingham aka the Penguin, is a well-known practitioner of LSD combined with walking breaks.
Arthur Lydiard wrote that LSD system of training does not reach the levels of effort most effective for building aerobic fitness. Pete Pfitzinger has written that the long slow distance method of training is acceptable for novice runners hoping to complete a marathon, but that more experienced runners benefit from long runs that, depending on the workout, incorporate a variety of paces including speeds approaching race pace. According to Pfitzinger, varying paces are necessary because different physiological adaptations, including increased glycogen storage and fat utilization, occur at specific training paces.
Galloway points out that if a runner wishes to increase their speed, interval training or speed training is recommended. Henderson uses races as speedwork and is a proponent of speedwork in limited quantities.
The scientific literature indicates that high-intensity training can provide greater benefit towards anaerobic capacity than moderate-intensity endurance training. The U.S. Army is reducing the use of long runs in its physical training programs.
This article has an unclear citation style.(March 2013)
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- Glover; Shepherd (1978). The Runner's Handbook.p.1
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- The Honolulu Marathon Clinic offers a shorter form of the rules:
- Train for at least an hour, three times a week.
- Train no more than four times a week.
- Pass the "talk" test while training.
- Drink water every 20 minutes HMC
- Parker-Pope, Tara; This Jogging Method Turns Out-of-Shape Into Runners Wall Street Journal, 25 May 2007. Access date: 2007-05-25
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- John Bingham, retrieved 2007-05-25
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- Military Playing Down Long Runs, Adopting More Diverse Fitness Programs