To bonk (or 'hit the wall') is to suffer a sudden, severe drop in energy during prolonged exercise when the body's carbohydrate stores (glycogen) become depleted, leaving you weak, lightheaded, and struggling to continue. Distinct from general fatigue, it's primarily a fueling failure, and it's prevented by eating carbohydrates regularly during long efforts and starting well-fueled.
Carb loading (carbohydrate loading) is the practice of eating extra carbohydrates in the days before an endurance event to maximize the glycogen stored in your muscles and liver — your primary fuel for prolonged exercise. By topping off these stores, runners delay glycogen depletion and the resulting 'bonk,' which is most beneficial for events lasting roughly 90 minutes or longer.
Zone 2 training is running (or other exercise) at a low, comfortable, aerobic intensity — roughly an easy, conversational effort — that builds the aerobic base by improving the body's ability to use fat for fuel and develop endurance with minimal fatigue. It underpins the popular '80/20' approach, in which the large majority of training is easy (zone 2) and only a small portion is hard.
VO2 max is the maximum rate at which your body can take in and use oxygen during intense exercise, measured in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). It represents your aerobic 'engine size' and is a key marker of endurance fitness. Influenced by genetics, it's also improved through training — especially high-intensity intervals — alongside threshold and base work.
Lactate threshold is the exercise intensity at which lactate begins to accumulate in the blood faster than the body can clear it, marking the upper limit of a pace you can sustain for a prolonged period. It's a key determinant of endurance performance — roughly the effort you could hold for about an hour — and is improved through threshold (tempo) training, raising your sustainable race pace.
A taper is the planned reduction in training volume in the days to weeks before a key race, allowing the body to recover, repair, and absorb the fitness built during hard training so you arrive fresh and strong. Intensity is usually maintained while overall mileage drops. A good taper boosts race-day performance; the restless, antsy feeling it causes is jokingly called 'taper madness.'
Power hiking is fast, deliberate, efficient uphill walking — often with hands pressing on the thighs or using poles — that trail and ultra runners use on steep climbs where it's nearly as fast as running but far less costly in energy. Knowing when to power hike instead of run is a core trail-running skill that conserves energy for the whole effort.
Cadence is the number of steps you take per minute while running (counting both feet). A higher cadence with shorter strides is generally associated with more efficient form, reduced overstriding, and lower impact and injury risk. While the often-cited '180 steps per minute' is a guideline rather than a rule, gradually increasing a very low cadence can improve running economy.
A negative split is completing the second half of a run or race faster than the first half. Considered an efficient, disciplined pacing strategy, it relies on starting conservatively to conserve energy and finishing strong, avoiding the early-pace blowups that lead to fading. On trails, where terrain varies, it's judged by effort rather than exact pace splits.
Hill repeats are a workout of repeated hard efforts up a hill, jogging or walking back down to recover, then repeating. They build leg and aerobic strength, power, and running economy, and prepare trail and mountain runners for climbing (vert). Often called 'speedwork in disguise,' hill repeats deliver high-intensity benefits with lower impact than flat sprints.