Thermal responses of rats exposed to continuous or intermittent 915 MHz mobile phone RF signals

The thermal effects of a mobile phone emitting radiofrequency electromagnetic fields (RF-EMFs) are well known, but the in vivo impact of different exposure patterns has not been directly demonstrated. This study aimed to compare the in vivo effects of continuous and intermittent exposure to 915 MHz LTE-modulated mobile phone signals under conditions that simulate typical mobile phone use. Male Sprague-Dawley rats were exposed either continuously at whole-body averaged specific absorption rates (SAR) of 0, 4, 6, or 8 W/kg, or intermittently at 0 or 8 W/kg using 10-min on/off cycles. Rectal and interscapular temperatures were recorded during 9 h of continuous exposure or 10 h of intermittent exposure. Comparisons were made under two matched conditions: continuous exposure at 8 W/kg for 5 h versus intermittent exposure at 8 W/kg for 10 h (equal RF-on time), and continuous 4 W/kg versus intermittent 8 W/kg (50% duty cycle; equal time-averaged SAR). Under equal cumulative RF-on time, intermittent 8 W/kg exposure caused only a brief temperature increase, whereas continuous 8 W/kg exposure resulted in a gradual and sustained rise. Under equal time-averaged SAR, continuous 4 W/kg showed no temperature change, whereas intermittent 8 W/kg caused a transient rise. No significant effects were observed at 6 W/kg continuous exposure, and sham groups remained stable. These findings provide direct, comparative in vivo evidence that both SAR level and exposure pattern significantly influence thermal outcomes during exposure to mobile phone RF signals.