Sport Science Glossary

Twenty years of coaching has taught me that the best sport science is the kind you can explain to an athlete in thirty seconds. This glossary is written for coaches, not textbooks. Every term is defined in plain language, with one practical sentence on how to actually use it.

Rate Of Force Development

How fast an athlete can produce force, not just how much. Think of two athletes who can both squat 400 pounds. The one who reaches peak force faster wins the race to the jump, the cut, or the first step. Coaches typically measure it in force plate tests like the isometric mid-thigh pull.

In practice: if your athletes are strong but slow, program for rate of force development with ballistic lifts and explosive intent, not more max strength work.

Reactive Strength Index

A measure of how well an athlete uses the stretch shortening cycle, calculated as jump height divided by ground contact time in a drop jump. A high index means the athlete lands and explodes off the ground quickly, which is the essence of sprinting and jumping. It separates the bouncy from the slow.

In practice: use reactive strength index to decide whether an athlete needs more stiffness work or more plyometric progressions before heavy loaded jumping.

RSI Modified

A version of the reactive strength index calculated from a countermovement jump instead of a drop jump, using time to takeoff rather than ground contact time. It is popular because the countermovement jump is already part of most testing batteries, so no extra drop jump test is required. It tells a similar story about explosiveness.

In practice: if you already run countermovement jumps on a force plate, you can track RSI modified for free and spot athletes whose jump strategy is getting slow or sloppy.

Countermovement Jump

A vertical jump where the athlete dips down first and then jumps. It is the most common jump test in sport, revealing jump height, peak power, and a stack of force plate metrics from a single test, and it is simple enough to run with a full roster. Nearly every monitoring program in the world uses it.

In practice: test the countermovement jump weekly or biweekly, track the trend rather than any single day, and look at strategy metrics, not just height.

Acute To Chronic Workload Ratio

A ratio comparing what an athlete did this week, the acute load, to what they have done on average over the past three to four weeks, the chronic load. It was designed to flag sudden spikes in training load that raise injury risk, though the evidence behind its exact thresholds is messier than the early headlines suggested. Treat it as a conversation starter, not a red light system.

In practice: when the ratio climbs well above 1.5, ask why before the week continues, and when it drops below 0.8, the athlete may be detraining.

Session RPE

The athlete's rating of perceived exertion for a whole session, multiplied by session duration to produce a single training load number. It is the simplest load measure ever invented, costs nothing, and works across every sport and training mode. Its weakness is honesty, since tired athletes and tough cultures skew the numbers.

In practice: collect session RPE within 30 minutes of every session, and compare it against your planned load to see whether the session you programmed is the session they experienced.

Internal Versus External Load

External load is the work done: meters run, tons lifted, jumps landed. Internal load is the athlete's response to that work: heart rate, RPE, soreness. The same external load can crush one athlete and barely register for another, which is the whole reason both matter. Coaching lives in the gap between the two.

In practice: when internal load climbs but external load stays flat, something is off. Check fatigue, illness, stress, or a readiness problem worth investigating.

Minimum Effective Dose

The smallest training dose that still produces the adaptation you want. It is the antidote to the more is better culture that buries athletes under volume they do not need. Every extra rep past the minimum effective dose costs recovery without buying much more performance.

In practice: before adding a set, a sprint, or a session, ask whether the current dose is failing, because if it is working, more is just more expensive fatigue.

Supercompensation

The theory that after training stresses the body, recovery carries performance slightly above its previous baseline before it settles back. It is the physiological logic behind tapering, deloads, and the entire idea of training cycles. The model is simplified, but the principle holds: stress, recover, adapt.

In practice: time your hardest training far enough from competition that the supercompensation window opens on game day, not the week after.

Periodization

The planned organization of training into phases so that different qualities peak at the right time. Linear, undulating, block, conjugate: the model matters less than the discipline of planning stress, recovery, and progression across a season. Periodization is really just decision making with a calendar.

In practice: write the whole season's plan before the first week, then adjust it weekly based on what your monitoring tells you, because the plan is a hypothesis, not a contract.

Velocity Based Training

Training that uses bar speed, measured with a device on the barbell, to guide load selection instead of fixed percentages. It auto regulates for daily readiness: a slow bar means back off, a fast bar means load up. It also gives athletes instant feedback, which sharpens intent on every rep.

In practice: use velocity to set working weights on the day rather than clinging to a spreadsheet percentage that assumed the athlete slept eight hours.

Force Plate

A platform that measures ground reaction forces during jumps, pulls, and isometric tests, producing the raw data behind metrics like peak force, rate of force development, and reactive strength index. It is the gold standard tool for neuromuscular assessment and has become affordable enough for most college and pro programs. A force plate does not coach for you. It just tells the truth faster.

In practice: pick two or three tests, run them consistently, and build your program around trends in the data, not single-day records.

Dynamic Strength Index

The ratio of an athlete's ballistic peak force, from a jump, to their maximal isometric force, from a mid-thigh pull. It shows how much of their strength they can actually express quickly. A low index means the athlete is strong but cannot use it. A high index means they use what they have.

In practice: a low dynamic strength index argues for ballistic and plyometric work, while a very high one argues for more maximal strength development.

Heart Rate Variability

The variation in time between consecutive heartbeats, used as a rough window into autonomic nervous system balance and recovery status. Higher variability generally signals a recovered, adaptable system, while suppressed variability can flag accumulated fatigue or stress. It is noisy and influenced by everything from illness to a bad night of sleep, so trends beat snapshots.

In practice: track morning heart rate variability against each athlete's own baseline and treat sustained drops as a prompt to check in, not a diagnosis.

Athlete Monitoring

The systematic collection of training, performance, and wellness data to guide coaching decisions. It can be as simple as daily wellness questionnaires and jump testing or as complex as GPS, force plates, and blood markers. The tool is never the point. The decisions are.

In practice: collect only what you will actually look at and act on, because data nobody uses is just paperwork with better branding.

Readiness

A snapshot of how prepared an athlete is to train or compete on a given day, built from sleep, soreness, mood, heart rate variability, jump data, or some combination. It is the daily answer to the question of whether to push today or pull back. Readiness is a guide, not a verdict, since athletes can perform through yellow lights.

In practice: use readiness scores to adjust the edges of a session, its volume and intensity, rather than to cancel training outright.

Taper

A planned reduction in training load before competition to shed fatigue while preserving fitness, so the athlete arrives fresh and sharp. Cut volume first and keep intensity. That is the classic recipe supported by decades of research. Get it wrong in either direction and you arrive flat or stale.

In practice: start the taper one to two weeks out for most team sport athletes, and resist the urge to sneak in one more hard session.

Deload

A short planned period of reduced training, usually a week, inserted within a training cycle to let fatigue dissipate. Unlike a taper, it is not aimed at a competition. It is maintenance for the training process itself. Skip deloads long enough and the body schedules one for you, usually as illness or injury.

In practice: program a deload every three to five weeks of hard training, and cut volume roughly in half while keeping movement quality high.

Post Activation Potentiation

The short term performance boost that can follow a heavy or explosive conditioning activity, like a heavy squat making the next few jumps higher. The mechanism involves neural and muscular priming, though fatigue from the conditioning activity competes with the effect. It is real but finicky, and highly individual.

In practice: if you use potentiation complexes, keep the conditioning activity heavy but low volume, rest three to seven minutes, and test whether each athlete actually responds before programming it.

Ground Contact Time

How long the foot spends on the ground during a step, hop, or jump landing, measured in milliseconds. Shorter contact times generally mean better stiffness and elastic ability, which is why sprinters live under 100 milliseconds while slow plyometrics run two to three times that. It is one of the simplest force plate or contact mat metrics to interpret.

In practice: cue hot ground and track contact times during plyometrics. If times drift long, the drill is too advanced for the athlete's current ability.

GPS Athlete Tracking

Wearable units that track position, speed, distance, and accelerations during field and court training, giving coaches the external load picture for every session. The headline metrics are total distance, high speed running, and sprint counts, plus the accelerations and decelerations that hammer the legs. The data is only as good as the satellite signal and the consistency of unit assignment.

In practice: give each athlete the same unit every session, define your speed zones once, and track weekly high speed running like a budget you cannot overspend.

Plyometrics

Jump training that exploits the stretch shortening cycle, from pogo hops to depth jumps, aimed at making athletes springier and faster off the ground. The magic is in short ground contacts and maximal intent, not in exhausting volume. Done poorly, plyometrics are just jumping tired. Done well, they are the closest thing to speed training in the weight room.

In practice: program plyometrics fresh, early in the session, with full recovery between sets, and progress intensity by task difficulty before adding volume.

Force Velocity Profile

A curve describing the trade off between how much force and how much velocity an athlete can produce, usually built from loaded jump testing. It shows whether an athlete is force dominant or velocity dominant relative to what their sport demands. Two athletes can jump the same height with completely different profiles, needing completely different training.

In practice: profile your athletes once or twice a year and let the result steer the next block toward heavy strength work or toward speed and ballistic work.

Change Of Direction

The ability to decelerate, redirect, and reaccelerate, which is what agility actually looks like in sport. It demands eccentric braking strength, technique, and the perceptual skill of reading the play, and the last of those cannot be trained with cones alone. Most agility drills train the feet and ignore the eyes.

In practice: build the physical base with eccentric strength and deceleration work, then add reactive, sport specific scenarios so the skill transfers to the game.

Wellness Questionnaire

A short daily survey asking athletes about sleep, soreness, fatigue, mood, and stress, usually on a simple scale. It is the cheapest monitoring tool in existence and often the most sensitive, because athletes feel problems before the data shows them. Its value depends entirely on honesty, which depends on trust and on coaches actually using the answers.

In practice: keep it under a minute, review it before every session, and visibly adjust training based on it so athletes learn that honest answers get honest coaching.