If you’ve ever browsed vertical jump training programs online, you’ve encountered a wall of numbers, abbreviations, and technical terminology. Sets, reps, rest intervals, intensity percentages, eccentric tempo, reactive strength index — these terms can be confusing or even intimidating to athletes who are new to structured training. But these numbers aren’t arbitrary; they encode important information about how to execute the program correctly and why each component produces specific adaptations. Understanding them helps you train smarter.
Sets and Reps: The Basic Structure of Training
Sets and reps are the fundamental unit of training prescription. A rep (repetition) is a single execution of an exercise. A set is a group of consecutive reps performed without rest. For accurate jump measurements, dunk calculator tools provide the exact figures you need. “3 sets of 5 reps” means performing 5 reps, resting, performing 5 more reps, resting, and then performing 5 final reps. For explosive exercises like plyometrics, low reps (1-5) per set are typical because each rep needs to be performed at maximum intensity — quality degrades significantly after more than 5 true maximum-effort reps.
Rest Periods and Why They Matter
Rest periods between sets are not suggestions to be shortened in the interest of time — they are training variables with specific physiological purposes. For maximum power and strength development, rest periods of 3 to 5 minutes are typically prescribed. These long rests allow the phosphocreatine energy system to fully restore, enabling maximum intensity on every set. Shorter rest periods (30-90 seconds) are appropriate for conditioning work but produce suboptimal results for maximum strength and power development.
Intensity Percentages and 1-Rep Max
Strength programs often prescribe intensity as a percentage of your 1-rep maximum (1RM) — the heaviest weight you can lift for exactly one rep. “80% of 1RM for 3 sets of 3” means you load the bar to 80% of your maximum squat, for example, and perform 3 reps in each of 3 sets. Regular 1RM testing allows you to set appropriate training weights and track strength gains over time. Online calculators can estimate 1RM from submaximal performances if you prefer not to test single-rep maxima.
Eccentric Tempo and Time Under Tension
Some programs specify the speed at which exercises should be performed using tempo notation. A notation like “3-1-1-0” for a squat means: 3 seconds to lower (eccentric phase), 1 second pause at the bottom, 1 second to stand up (concentric phase), and 0 seconds at the top before the next rep. Eccentric loading — deliberately slowing the lowering phase — increases time under tension and develops tendon strength and muscle cross-sectional area more effectively than fast, uncontrolled lowering.
Reactive Strength Index (RSI)
Reactive strength index (RSI) is a key performance metric specifically relevant to jumping athletes. It’s calculated by dividing jump height by ground contact time — essentially measuring how efficiently an athlete uses the stretch-shortening cycle. A high RSI indicates that an athlete jumps high while spending minimal time on the ground, which is the athletic quality that translates best to explosive jump performance. Improving RSI is a specific goal of depth jump training and high-speed reactive drills.
Periodization: The Big Picture of Training Structure
Periodization refers to the planned, systematic variation of training variables over time to optimize performance while managing fatigue. Most sophisticated jump programs include phases of different emphasis — hypertrophy, maximum strength, power conversion, and peaking — each lasting several weeks. This phased approach allows each quality to be developed sequentially, with earlier phases building the foundation for later ones. Understanding periodization helps you see how individual training sessions fit into a larger developmental arc.