A swimmer training apparatus includes a housing having a rotatable spool mounted therein and defining a longitudinal spool axis. Test signal data is supplied by an external source. The filter filters the input signal, thereby generating a filtered signal. The phase generator provides in the first mode each of the gate signals the control signal and the respective other gate signal. A plurality of circumferentially spaced-apart longitudinal grooves are provided on the second portion adjacent its intersection with the shaft portion. In a heat assisted recording and reproduction method using such a magnetic storage medium, during reproduction, the SN ratio in a reproduction signal is enhanced by optimizing the bias current applied to the head using magneto-resistance effect.