Fartlek is a form of running training — Swedish for 'speed play' — that blends continuous running with bursts of faster effort in an unstructured, by-feel way, rather than the rigid timed repetitions of formal intervals. By spontaneously varying pace (for example, surging to the next tree), fartlek builds both aerobic and anaerobic fitness while staying flexible and enjoyable, making it well suited to varied trail terrain.
Intervals (interval training) are a workout method that alternates periods of hard, faster running with periods of easier running or rest to recover, repeated for several reps. By spending time at higher intensities than continuous running allows, intervals build speed, VO2 max (aerobic power), running economy, and the ability to sustain hard efforts. A cornerstone of structured training, interval workouts are defined by the work duration/intensity, the recovery, and the number of reps.
A tempo run is a sustained running effort at a 'comfortably hard' pace — typically around your lactate threshold — held for an extended period (often 20–40 minutes). By training the body to clear lactate efficiently, tempo runs raise the pace you can sustain before fatigue sets in, making them a cornerstone workout for building endurance and race performance.
The long run is the longest run of a runner's training week, typically run at an easy, conversational pace, designed to build aerobic endurance, strengthen the cardiovascular system and muscles, improve fat-burning efficiency, and prepare the body and mind for sustained distance. A cornerstone of nearly every distance-running and trail-running training plan, the long run is gradually lengthened over time and is especially central to marathon and ultramarathon preparation.
Chafing is painful skin irritation caused by repeated friction — skin rubbing against skin, clothing, or gear — often worsened by moisture, sweat, and salt. Common on long hikes and runs at the inner thighs, underarms, nipples, and under pack straps, it ranges from mild redness to raw, broken skin. It is largely preventable with the right clothing, lubricants, and fit.
A trail rating is a classification of a trail's overall difficulty, commonly expressed as easy, moderate, difficult (strenuous), or similar categories, based on factors like distance, elevation gain, steepness, and terrain. Trail ratings help hikers and runners choose routes that match their fitness and experience. However, ratings are not standardized across agencies and apps, so the same label can mean different things in different places.
Fell running is the sport of running on steep, rough, open upland and mountain terrain — 'fells' being the hills and mountains of northern Britain, where the sport originated. Characterized by steep climbs and descents, often pathless and unmarked terrain, harsh weather, and a strong self-reliance and navigation ethic, fell running is a hardier, more mountainous cousin of trail running, with a distinctive British heritage and racing culture.
A hundred-miler is a 100-mile (about 161 km) ultramarathon — a benchmark distance in ultrarunning that typically takes from under half a day for elites to around 24–48 hours for most finishers, usually run through at least one night. These races, often on mountainous trails, demand months of training, careful pacing and fueling, sleep and night-running management, and the support of aid stations, crews, and pacers. Finishing a hundred-miler is a celebrated milestone in the sport.
A cutoff is a time limit in a race — particularly ultramarathons — by which a runner must reach a particular checkpoint or aid station, or else they are pulled from the race (a 'time-out' DNF). Cutoffs exist for runner safety, logistics, and to keep the event on schedule. Intermediate cutoffs at points along the course, plus an overall finish cutoff, mean runners must maintain a minimum pace, making cutoff management a key strategic concern in long races.
DNF stands for 'Did Not Finish' — a race result indicating that a participant started the event but did not complete it, whether by dropping out voluntarily or by missing a cutoff. Common in long and demanding races like ultramarathons, a DNF can result from injury, illness, exhaustion, stomach issues, weather, or simply running out of time. Though disappointing, a DNF is a normal part of endurance racing, and sometimes the wise, safe choice.
