Freediving Disciplines 

• Static Apnea (STA) – Holding one’s breath for as long as possible while face down and motionless at the surface.
  
• Dynamic Apnea (DYN) – Swimming horizontally underwater for distance with monofin or bi‑fins.
  
• Dynamic No Fins (DNF) – Swimming underwater distance without fins .
  
• Constant Weight (CWT) – Diving vertically with the same weight down and up using bi‑fins or monofin.
  
• Constant Weight Bi‑fin (CWTB) – Separate bi‑fin category without dolphin kick; no rope or ballast assist allowed.
  
• Constant Weight No Fins (CNF) – Diving down and up using only arms and legs, no fins.
  
• Free Immersion (FIM) – Pulling down and up along a rope, same weight throughout, no fins.
  
• Variable Weight (VWT) – Descending with weight or sled, then ascending by pulling or finning.
  
• No Limits (NLT) – Deepest discipline: descent via weighted sled, ascent via an inflatable lift bag; highly dangerous and not AIDA‑sanctioned. It is not recognised in competitions due to its high-risk nature. 

Physiology & Risk Factors

• Apnea – Voluntary breath‑hold; cessation of breathing.
  
• Mammalian Diving Reflex – Automatic physiological response (bradycardia, vasoconstriction, spleen contraction) triggered by face immersion in cold water.
  
• Blood Shift – Redistribution of blood to chest and head to protect organs under pressure.
  
• Bradycardia – Slowed heart rate, part of diving reflex
  
• Hypercapnia – Elevated CO₂ levels in the blood, like carbon dioxide toxicity.
  
• Hypoxia – Insufficient oxygen reaching body tissues, leading to blackout.

Safety & Emergencies

• Loss of Motor Control (LMC / “Samba”) – Involuntary muscle spasms signaling critical oxygen depletion.
  
• Blackout – Loss of consciousness from cerebral hypoxia, often without warning, possibly during ascent or on the surface.
  
• Shallow-Water Blackout (SWB) – Blackout occurs near the surface in shallow dive due to hyperventilation‑induced hypocapni

Equipment & Techniques

• Frenzel Equalization – Preferred equalization method using tongue to pump air into ear via blocked nostrils.
  
• Valsalva Equalization – Pushing air from lungs by diaphragm against pinched nostrils; less efficient, gas‑wasting.
  
• Mouthfill – Advanced equalization technique for very deep dives: air stored in mouth to equalize beyond 40 m.
  
• Low‑Volume Mask / Fluid Mask – Masks with minimal internal air volume for easier equalization; fluid-filled masks use water inside the lens to correct distortion.
  
• Snorkel – Simple breathing tube used between dives at the surface.
  
• Weight Belt / Neck Weight – Lead weights to adjust buoyancy; neck weight helps with proper trim and descent initiation.
  
• Lanyard – Safety line between diver and rope to prevent getting lost or disoriented.

Lung Volumes & Breath Techniques

• Total Lung Capacity (TLC) – Max volume in lungs after full inhalation.
  
• Vital Capacity (VC) – Max inhaled and exhaled volume during effort.
  
• Residual Volume (RV) – Air remaining in lungs after forceful exhalation.
  
• Functional Residual Capacity (FRC) – Air volume left after passive exhale (ERV + RV); basis for exhale‑diving training.
  
• Packing / Lung Packing – Glossopharyngeal insufflation to overfill lungs; advanced technique with risks.

Other Key Terms

• Barotrauma (Squeeze) – Damage to air‑filled cavities (ears, mask, sinuses, lungs) due to unequal pressure.
  
• Sinus Squeeze – Painful pressure imbalance in sinus cavities while descending.
  
• Cramps – Painful involuntary muscle contractions, often in legs during long dives.
  
• Recovery Breathing – Active inhalation and passive exhalation pattern immediately after a dive to normalize O₂/CO₂ levels.
  
• Free Fall / Sink Phase – Short glide after reaching neutral or negative buoyancy, finless descent to depth for efficiency.
  
• Countdown Time – Time called out before static apnea to coordinate breath‑up and relaxation.
  
• Spotting – A qualified buddy or judge watching a diver for safety during training or competition.