Bonking (also called 'hitting the wall') is the sudden, severe fatigue that strikes when the body depletes its stored carbohydrate (glycogen), leaving the muscles and brain without their primary quick fuel. Common in endurance running and cycling, the bonk brings profound weakness, heavy legs, dizziness, and mental fog. It is largely preventable by fueling consistently with carbohydrates during prolonged efforts and starting well-fueled.
Carb-loading (carbohydrate loading) is the practice of increasing carbohydrate intake in the days before a long endurance event to maximize the glycogen stored in the muscles and liver — the body's most accessible fuel for sustained, harder efforts. By topping up these glycogen stores, carb-loading helps delay the depletion and 'bonk' that occur when fuel runs low, improving endurance performance in events lasting roughly 90 minutes or longer.
Zone 2 is the second of the common heart-rate (or effort) training zones — an easy, comfortable, conversational intensity, low enough to sustain for long periods and to keep a conversation going. Training in Zone 2 builds the aerobic base: it develops the cardiovascular system, increases mitochondria and capillaries, and improves the body's ability to burn fat for fuel. The principle that most endurance training should be easy (much of it in Zone 2) is foundational to endurance development.
VO2 max is the maximum rate at which a person's body can take in, transport, and use oxygen during intense exercise, measured in milliliters of oxygen per kilogram of body weight per minute. It represents the ceiling of your aerobic power and is a key indicator of cardiovascular fitness and endurance potential. Determined by genetics and training, VO2 max can be improved with high-intensity training, and along with lactate threshold and economy, it shapes endurance performance.
Lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the blood faster than the body can clear it, marking the transition from a pace you can sustain for a long time to one that leads to rapid fatigue. It's a key determinant of endurance performance — roughly the fastest pace you can hold for about an hour — and is highly trainable, making it a central target of structured endurance training through tempo and threshold workouts.
A taper is the planned reduction in training volume in the days or weeks before a race, designed to let the body recover from accumulated training fatigue, repair, and replenish energy stores so the runner arrives at the start line rested and ready to perform. Training intensity is usually maintained while volume drops. A well-executed taper can produce measurable performance gains, while too much or too little tapering can leave a runner flat or fatigued.
Power hiking is fast, efficient, purposeful walking up steep terrain, used by trail runners and mountain athletes on climbs too steep to run efficiently. On steep grades, power hiking is often nearly as fast as running but far more energy-efficient, so even elite runners power hike the steepest sections of trail and ultra races. The technique uses a strong, driving stride, often with hands pressing on the thighs (or trekking poles) for power.
Cadence is a runner's step rate — the number of steps taken per minute (spm). It's a key measure of running form: a higher cadence with shorter strides generally reduces overstriding and impact, which can improve efficiency and lower injury risk. While '180 spm' is a popular target, optimal cadence varies by individual, speed, and terrain, and is best improved gradually.
A negative split is a pacing strategy in which a runner completes the second half of a race or run faster than the first half. By starting conservatively and finishing strong, negative splitting helps conserve energy, avoid early burnout, and often produces better overall times and a stronger finish. It's a widely recommended approach, though on trails it's measured by effort rather than exact pace due to varying terrain.
Hill repeats are a workout consisting of repeated hard efforts running uphill, each followed by an easy jog or walk back down to recover, repeated for several reps. By combining intensity with the resistance of the incline, hill repeats build leg strength and power, improve running economy and form, boost aerobic fitness, and prepare runners for climbing — all with less impact than flat speedwork. They're a staple workout, especially valuable for trail and mountain running.
