The Intervals.icu API supports updating and reading all of the wellness fields:
public Float weight;
public Integer restingHR;
public Float hrv; // rMSSD
public Float hrvSDNN;
public MenstrualPhase menstrualPhase;
public Integer kcalConsumed;
public Integer sleepSecs;
public Float sleepScore;
public Integer sleepQuality; // Poor(4), Avg(3), Good(2), Excellent(1)
public Float avgSleepingHR;
public Integer soreness; // None(0), Low(1), Avg(2), High(3), Extreme(4)
public Integer fatigue; // None(0), Low(1), Avg(2), High(3), Extreme(4)
public Integer stress; // None(0), Low(1), Avg(2), High(3), Extreme(4)
public Integer mood; // Poor(4), Avg(3), Good(2), Excellent(1)
public Integer motivation; // Poor(4), Avg(3), Good(2), Excellent(1)
public Integer injury; // Injured(4), Poor(3), Niggle(2), Excellent(1)
public Float spO2; // 0-100%
public Integer systolic; // blood pressure mmHg
public Integer diastolic;
public Integer hydration; // Well Hydrated (1), Hydrated(2), Dehydrated(3), Very Dehydrated(4)
public Float hydrationVolume; // litres consumed
public Float readiness;
public Float baevskySI;
public Float bloodGlucose; // mmol/L
public Float lactate; // mmol/L
public Float bodyFat; // %
public Float abdomen; // cm
public Float vo2max; // ml/kg/min
public String comments;