This paper proposes a simple, but efficient, adaptive space-time-frequency coded (STFC) multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) system to improve the average BER performance for body-to-external link wireless body area network (WBAN) applications. The novelty of this paper is the proposed body direction based adaptive algorithm that controls the set of modulation scheme, space-time-frequency code (STFC) coding rate, and power of signal constellations implemented in STFC MB-OFDM UWB WBAN. Simulation results show that the proposed system can provide a consistent 1-2 dB improvement in the case of 2I1O configuration, and 1-3 dB improvement in a medium-to-high SNR region in the case of 2I2O configuration, compared to the non-adaptive system. The improvement practically means a possible reduction of 12.5% - 50% of the total transmitted power to achieve the similar performance as the non-adaptive system. In other words, it can save significantly the power consumption and prolong the battery life of WBAN devices.