{
  "resourceType": "ActivityDefinition",
  "id": "skull-crusher",
  "url": "https://bodyiq.dev/fhir/ActivityDefinition/skull-crusher",
  "version": "1",
  "name": "SkullCrusher",
  "title": "Skull Crusher (Lying Triceps Extension)",
  "status": "draft",
  "experimental": true,
  "description": "Lie supine on a flat bench holding an EZ-curl bar or dumbbells with arms extended over the chest, shoulders flexed to roughly 90 degrees. Keeping the upper arms still, bend only the elbows to lower the load under control toward the forehead or just behind the crown of the head, then extend the elbows back to the start without letting the elbows flare or drift.",
  "useContext": [
    {
      "code": {
        "system": "http://terminology.hl7.org/CodeSystem/usage-context-type",
        "code": "user"
      },
      "valueCodeableConcept": {
        "text": "difficulty: intermediate"
      }
    }
  ],
  "topic": [
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "skull-crusher",
          "display": "Skull Crusher (Lying Triceps Extension)"
        }
      ]
    }
  ],
  "bodySite": [
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "elbow",
          "display": "Elbow"
        },
        {
          "system": "http://snomed.info/sct",
          "code": "44034005",
          "display": "Structure of humeroulnar joint"
        }
      ],
      "text": "Elbow"
    }
  ],
  "kind": "ServiceRequest",
  "dosage": [
    {
      "text": "For hypertrophy: 2-4 sets of 8-12 repetitions at moderate load, 2-3 sessions per week, consistent with general resistance-training guidelines; for strength emphasis, 3-5 reps at higher load once technique is stable."
    }
  ],
  "usage": "Evidence: limited. Surface EMG comparisons of common triceps exercises show the lying triceps extension produces moderate-to-high triceps brachii activation, though generally below weighted dips, close-grip pressing, or bodyweight extensions in some comparisons. Because the shoulder is held in flexion, the long head works at a longer muscle length than in pressdown variants, and recent longitudinal work on stretch-position training suggests long-length loading of the triceps (e.g., overhead or behind-the-head variants) may favor greater long-head hypertrophy. Wrist and shoulder stabilizer activity is modest and primarily isometric.",
  "note": [
    {
      "text": "Imagine your upper arms are pillars set in concrete — only your forearms move."
    },
    {
      "text": "Lower the bar toward the top of your head, then push it back up toward the ceiling, not toward your feet."
    },
    {
      "text": "Keep your elbows pointing at the ceiling and shoulder-width apart; don't let them flare out."
    },
    {
      "text": "Take 2-3 seconds to lower, then extend smoothly without bouncing out of the bottom."
    }
  ],
  "extension": [
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Triceps Brachii"
        },
        {
          "url": "role",
          "valueCode": "primary"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "40284004"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Anconeus"
        },
        {
          "url": "role",
          "valueCode": "synergist"
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Anterior Deltoid"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "35259002"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Pectoralis Major"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "60005003"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Flexor Carpi Radialis"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "30339000"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Flexor Carpi Ulnaris"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "14437004"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Biceps Brachii"
        },
        {
          "url": "role",
          "valueCode": "lengthening"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "16225001"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Brachialis"
        },
        {
          "url": "role",
          "valueCode": "lengthening"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "75915005"
          }
        }
      ]
    }
  ]
}