Sources and original illustrations

Primary references and the limits of this educational collection.

Primary references

• CDC: Adult Activity Overview — Adult activity guidance includes aerobic activity and strengthening all major muscle groups.
• ACSM: Updated 2026 Resistance Training Guidelines — Individualized training, consistency, equipment options and limits of advanced techniques for healthy adults.
• NSCA: Types of Resistance Training Equipment — Machine and free-weight differences, adjustment, fit and equipment demands.
• MedlinePlus: Exercise and Physical Fitness — Exercise types, gradual participation and seeking advice when safety is uncertain.
• NIAMS: Sports Injuries — Injury symptoms, risk factors and the limits of self-assessment.
• MedlinePlus: Muscle Aches — Muscle pain has multiple causes and concerning symptoms require appropriate care.
• NIA: Types of Exercise and Physical Ability — Strength activity, breathing without holding the breath and different activity roles.
• NIH ODS: Supplements for Exercise and Athletic Performance — Supplement evidence, safety, interactions and product limitations.
• NSCA: Certification Verification — Checking a claimed NSCA credential through its issuing organization.
• NHLBI: Physical Activity and Your Heart — Different forms of physical activity and broader health context.
• NIAMS: Sports Injuries, Diagnosis and Steps to Take — Professional assessment and individualized care for suspected injuries.

Original visual material

The diagrams in this edition are original SVG illustrations explaining the sequence or decisions in each guide. They do not show a laboratory experiment, a personal trip or a tested product result. No photographs from the linked sources are reproduced.

Check the source in context

References were consulted during preparation of this edition. A source may cover a broader or narrower question than a particular guide; the support notes above explain why it is listed. Read the original for methodology, exceptions and updates.