private Metabolism getUserData() {
		// Get data from user
		if(!femaleButton.isSelected() && !maleButton.isSelected()) {
			JOptionPane.showMessageDialog(frame, "You must select a gender.", "Error", JOptionPane.ERROR_MESSAGE);
			return null;
		}
		Gender gender = femaleButton.isSelected()? Gender.Female : Gender.Male;
		int age = 0;
		try {
			age = Integer.parseInt(ageTextField.getText());
		} catch(NumberFormatException ex) {
			JOptionPane.showMessageDialog(frame, "The age must be an integer.", "Error", JOptionPane.ERROR_MESSAGE);
			return null;
		}
		double height, weight, lpa;
		try {
			height = Double.parseDouble(heightTextField.getText());
			weight = Double.parseDouble(weightTextField.getText());
			lpa = Double.parseDouble(lpaTextField.getText());
		} catch(NumberFormatException ex2) {
			JOptionPane.showMessageDialog(frame, "The weight, the height and the level of physical activities must be a double.", "Error", JOptionPane.ERROR_MESSAGE);
			return null;
		}

		// Notify model of changes
		Metabolism m = null;
		try {
			m = new Metabolism(weight, height, age, gender, lpa);
		} catch (Exception e) {
			JOptionPane.showMessageDialog(frame, e.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
		}

		return m;
	}