How to keep iwatch app active to transfer motion & health data – Ios swift

Here is my solution that can help you:

Ref: https://developer.apple.com/documentation/healthkit/workouts_and_activity_rings/running_workout_sessions

1. Setup HKWorkoutSession and CoreMotion listener

import WatchKit
import Foundation
import CoreMotion
import HealthKit

enum VelocityVector: Int {
    case x, y, z
}

class InterfaceController: WKInterfaceController {

    @IBOutlet weak var labelVelocity: WKInterfaceLabel!
    let coreMotion = CMMotionManager.init()
    let pool = OperationQueue.init()
    let currentSession: HKWorkoutSession?
    let healthKit = HKHealthStore()
    
    override func awake(withContext context: Any?) {
        coreMotion.accelerometerUpdateInterval = 0.1
        coreMotion.startAccelerometerUpdates(to: pool) { data, err in
            guard let _data = data else { return }
            DispatchQueue.main.async {
                self.labelVelocity.setText(String.init(format: "G-Force (x:y:z) %.3f:%.3f:%.3f", arguments: [_data.acceleration.x, _data.acceleration.y, _data.acceleration.z]))
            }
        }
        
        let config = HKWorkoutConfiguration.init()
        config.activityType = .other
        config.locationType = .unknown
        
        do {
            self.currentSession = try HKWorkoutSession.init(healthStore: self.healthKit, configuration: config)
            self.currentSession?.startActivity(with: Date())
        } catch error {
            print(error?.localizedDescription)
        }        
    }

    private func stopHKWorkoutSession() {
        self.currentSession?.stopActivity(with: Date())
        self.currentSession?.end()
    }
    
    override func willActivate() {
        // This method is called when watch view controller is about to be visible to user
    }
    
    override func didDeactivate() {
        // This method is called when watch view controller is no longer visible
    }

}

2. Enable "Workout processing" in Background Mode: