How to pre-select radiobutton- / checkbox-group in the playframework?

I am trying to construct a simple form with the Play!Framework 2.3.8. Therefore I have created a radiobutton group, which works fine, but how do you pre-select a certain radiobutton?

I did not find anything for this in the documentation:

Documentation radiobuttons

The same problem exists for checkboxes:

Documentation checkboxes

@helper.form(action = routes.Application.submit(), 'id -> "userForm"){
        <fieldset>
            @helper.inputRadioGroup(
            userForm("Geschlecht"),
            options = options("Mann"->"Mann","Frau"->"Frau"),
            '_label -> "Gender",
            '_error -> userForm("Geschlecht").error.map(_.withMessage("select gender"))
            )
        </fieldset>

Any ideas?