{
  "resourceType": "ActivityDefinition",
  "id": "crunch",
  "url": "https://bodyiq.dev/fhir/ActivityDefinition/crunch",
  "version": "1",
  "name": "Crunch",
  "title": "Crunch",
  "status": "draft",
  "experimental": true,
  "description": "Lie supine with knees bent about 90 degrees and feet flat on the floor, hands lightly supporting the head or crossed over the chest. Exhale and curl the trunk, lifting the head and shoulder blades off the floor by flexing the spine — drawing the ribs toward the pelvis — while the low back stays in contact with the floor. Lower back down with control; unlike a full sit-up, the movement stops well short of sitting upright, which limits hip flexor involvement.",
  "useContext": [
    {
      "code": {
        "system": "http://terminology.hl7.org/CodeSystem/usage-context-type",
        "code": "user"
      },
      "valueCodeableConcept": {
        "text": "difficulty: beginner"
      }
    }
  ],
  "topic": [
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "crunch",
          "display": "Crunch"
        }
      ]
    }
  ],
  "bodySite": [
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "thoracic-spine",
          "display": "Thoracic Spine"
        },
        {
          "system": "http://snomed.info/sct",
          "code": "5261000",
          "display": "Structure of thoracic intervertebral disc"
        }
      ],
      "text": "Thoracic Spine"
    },
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "lumbar-spine",
          "display": "Lumbar Spine"
        },
        {
          "system": "http://snomed.info/sct",
          "code": "23526008",
          "display": "Structure of lumbar intervertebral disc"
        }
      ],
      "text": "Lumbar Spine"
    },
    {
      "coding": [
        {
          "system": "https://bodyiq.dev/fhir/CodeSystem/exercise",
          "code": "pelvis",
          "display": "Pelvis"
        }
      ],
      "text": "Pelvis"
    }
  ],
  "kind": "ServiceRequest",
  "dosage": [
    {
      "text": "2-3 sets of 10-20 controlled repetitions, 2-3 sessions per week, consistent with general resistance-training guidelines for trunk musculature; progress by adding load or lever length rather than high-repetition volume."
    }
  ],
  "usage": "Evidence: moderate. Surface EMG studies consistently show the crunch produces high rectus abdominis activation and moderate external and internal oblique activation, and it compares favorably with — or exceeds — many commercial abdominal devices. Compared with a full sit-up, the shortened range keeps hip flexor (iliopsoas/rectus femoris) activity substantially lower, which is why the crunch is preferred when lumbar shear from hip flexor pull is a concern. Claims of selectively isolating the \"upper\" versus \"lower\" rectus abdominis with crunch variants are not well supported; regional differences reported across studies are small and inconsistent. Hands-behind-head performance tends to increase sternocleidomastoid recruitment if the head is pulled, which is a technique fault rather than a training target.",
  "note": [
    {
      "text": "Draw your ribs down toward your pelvis as you curl up."
    },
    {
      "text": "Peel your shoulder blades off the floor, then lower back down one segment at a time."
    },
    {
      "text": "Keep a fist-sized gap between your chin and chest — don't pull on your head with your hands."
    },
    {
      "text": "Exhale as you curl up, inhale as you lower."
    }
  ],
  "extension": [
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Rectus Abdominis"
        },
        {
          "url": "role",
          "valueCode": "primary"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "31243008"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "External Oblique"
        },
        {
          "url": "role",
          "valueCode": "secondary"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "1179024003"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Internal Oblique"
        },
        {
          "url": "role",
          "valueCode": "secondary"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "1179024003"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Transversus Abdominis"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "86493009"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Sternocleidomastoid"
        },
        {
          "url": "role",
          "valueCode": "synergist"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "22823000"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Erector Spinae Group"
        },
        {
          "url": "role",
          "valueCode": "lengthening"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "44947003"
          }
        }
      ]
    },
    {
      "url": "https://bodyiq.dev/fhir/StructureDefinition/muscle-involvement",
      "extension": [
        {
          "url": "muscle",
          "valueString": "Iliopsoas"
        },
        {
          "url": "role",
          "valueCode": "stabilizer"
        },
        {
          "url": "coding",
          "valueCoding": {
            "system": "http://snomed.info/sct",
            "code": "68455001"
          }
        }
      ]
    }
  ]
}