NOVELTY - The device (1) has a holder (2) with a display (2a) and a wearable/implantable element (400) by a sensor (4) to detect a heart rate of a user in a preset period of time of wakefulness and/or sleep of user. A processing unit is adapted for defining an aerobic threshold of user and a detected state of psycho-physical stress in the knowledge of heart rate variability (HRV) parameter. A workout program for the user and/or parameter representative of the intensity of workout that user must carry out in relation to the determined aerobic threshold value and level of stress is generated.    USE - Device for monitoring physiological parameter of user in exercise machine (claimed).    ADVANTAGE - The device which is provided allows the user to use the HRV parameter related to heart rate to manage in the best and most appropriate way all the activities to be performed during the day with reference to physical workout activity. The user is allowed to obtain a correct and precise indication about the intensity and ways of the workout to carry out in relation to the conditions of stress and to take into account the energy balance between ingested calories and burnt calories. The ability of the device to provide immediate and intuitive indications to allow the user to behave properly in relation to the conditions without having to carry out further investigations or analyses is further increased. The user is allowed to know his own conditions and his level of psycho-physical stress immediately before starting the workout so as to be able to train in the most appropriate way without harming his own health. Hence the user sets the exercise machine in a manner consistent with his current psycho-physical condition. The device possibly devoid the units for measuring physical activity as the activity is detected directly by the sensors present on the exercise machine. Thus the data stored on the device and the information provided by the processing unit is displayed and/or managed easily through the user interface of the exercise machine while carrying out the exercise.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a method for control and management of the operation of the device; and    (2) a computer program for control and management of the operation of the device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic front view of a monitoring device.    Device for monitoring physiological parameter of user (1)    Holder (2)    Display (2a)    Sensor (4)    Wearable/implantable element (400)