Energy Systems and Physiology

ISSA CPT Study Guide Exam

Track your progress as you read

Finished sections get a check mark.

1 Exam Map and Applied Science

ISSA CPT Exam Format and Blueprint Functional Anatomy and Biomechanics Muscle Actions and Planes of Motion Energy Systems and Physiology Cardiorespiratory Systems and Training Adaptations

2 Nutrition and Assessment

Nutrition: Macros and Hydration Supplements and Special-Population Nutrition Client Consultation and Goal Setting Fitness Assessments and Screening Movement Screens and Posture

3 Program Design

Program Design Principles and Periodization Resistance Training Variables Cardio Programming and Zones Flexibility, Mobility, and Recovery Special Populations Program Modifications

4 Exercise Technique

Squat, Hinge, and Lower-Body Technique Push, Pull, and Upper-Body Technique Core, Balance, and Stability Training Cueing, Spotting, and Error Correction Progressive Overload and Regression

5 Professional Practice and Exam Day

Scope, Ethics, and Professional Responsibility Business, Liability, and Client Records Behavior Change and Adherence ISSA CPT Exam Strategy and Review

Energy Systems and Physiology

Key Takeaways Explain This Topic AI

ATP is the immediate energy currency; phosphagen (ATP-PC), glycolytic, and oxidative systems replenish it at different rates.

The phosphagen system dominates efforts under ~10 seconds (max lift, sprint); glycolysis fuels 30 seconds to 2 minutes of high intensity.

The oxidative system uses oxygen to metabolize fats and carbohydrates for prolonged submaximal work.

Lactate is a fuel substrate, not purely a waste product; accumulation correlates with hydrogen ion buildup and fatigue sensation.

Training specificity demands matching energy-system stress to client goals and sport demands.

Last updated: September 2026

Quick Answer: Three energy systems supply ATP: phosphagen (0–10 sec, max power), glycolytic (moderate-high intensity, limited duration), and oxidative (aerobic, sustained). They overlap—no exercise uses only one. Program cardio and resistance rest intervals to target the system matching client goals.

Energy Systems and Physiology

Exercise physiology questions on the NCCPT CPT exam test whether you can match rest intervals, set durations, and modality choices to the dominant energy pathway—not whether you can recite Krebs cycle intermediates.

ATP: The Universal Currency

Adenosine triphosphate (ATP) powers muscle cross-bridge cycling. Intramuscular ATP stores last roughly 1–2 seconds . Three systems resynthesize ATP at different speeds and capacities:

System Duration Intensity Byproducts Example Activity
Phosphagen (ATP-PC) 0–10 sec Maximal Creatine, ADP, Pi 1RM attempt, 40-m sprint
Glycolytic (anaerobic) ~10 sec – 2 min High Lactate, H+, heat 400-m run, HIIT round
Oxidative (aerobic) >2–3 min Low–moderate CO₂, H₂O, heat Distance jog, steady cycling

Systems work concurrently with proportional contribution shifting as duration increases.

Phosphagen System Training

Rest intervals of 2–5 minutes between maximal strength sets allow phosphocreatine resynthesis (~80% in 3 minutes, ~95% in 5 minutes for trained individuals). This supports strength and power programming with loads ≥85% 1RM.

Glycolytic Training

Intervals of 20–90 seconds at 85–95% max heart rate with 1:2 to 1:3 work-rest ratios stress glycolysis. Useful for field sports and metabolic conditioning. Excessive glycolytic volume without recovery elevates overtraining risk in general-population clients.

Oxidative Training

Steady-state cardio at 60–70% HRmax (Zone 2) improves mitochondrial density, capillarization, and fat oxidation efficiency. Long slow distance builds aerobic base for deconditioned clients before high-intensity progressions.

Lactate and Fatigue

Blood lactate rises when glycolytic flux exceeds mitochondrial clearance. Modern physiology treats lactate as a shuttle fuel oxidized by Type I fibers and heart muscle. The burn associates more with hydrogen ion (H+) accumulation lowering pH. Trainers use lactate threshold or ventilatory threshold concepts to set tempo-run pace—not to frighten clients about "toxic lactate."

Muscle Fiber Types

Fiber Characteristics Training Response
Type I (slow oxidative) Fatigue-resistant, aerobic Endurance volume
Type IIa (fast oxidative-glycolytic) Versatile Mixed training
Type IIx (fast glycolytic) High force, fatigues quickly Power, heavy loads

Fiber type shifts are modest in adults—training mainly hypertrophies existing fibers and improves neural efficiency rather than converting IIx to Type I.

Worked Scenario: Rest Interval Selection

Client goal: increase 5RM back squat. Working sets at 85% 1RM for 3–5 reps require phosphagen dominance. Prescribe 3–5 minute rest between sets. If the same client later trains metabolic conditioning, shift to 30-second kettlebell swings with 90-second rest—glycolytic emphasis.

Hormonal and Neural Adaptations (Overview)

Resistance training elevates growth hormone and testosterone acutely post-session; chronic hypertrophy depends on total training volume, protein intake, and sleep. Neural adaptations (motor unit recruitment, rate coding, intermuscular coordination) dominate early strength gains in novices—often 6–8 weeks before significant hypertrophy appears.

Exam Traps

Trap: Believing aerobic exercise does not use phosphagen at start—first seconds of any activity tap ATP-PC.

Trap: Recommending 30-second rest for maximal strength sets—insufficient PCr recovery.

Trap: Stating fat burns only in the "fat-burning zone." Fat oxidation contributes at multiple intensities; total caloric deficit drives weight loss.

FITT Application to Energy Systems

Goal Frequency Intensity Time Type
Strength 3–4×/week ≥85% 1RM Short sets Compound lifts
Power 2–3×/week Explosive, submax load 1–5 reps Olympic derivatives, jumps
Endurance 3–5×/week 60–80% HRmax 20–60+ min Run, cycle, swim

Energy-system literacy connects program design to physiology —a core ISSA integration skill tested throughout the CPT exam.