Existing low-power MAC protocols only provide low throughput because of the fixed low duty-cycle. This often leads to poor performance when dealing with time-constrained burst traffic. In this paper, we propose a new hybrid CSMA/TDMA MAC protocol, called Queue-MAC, that dynamically adapts the duty-cycle according to the current network traffic. The queue length of nodes is used as the network traffic indicator. When the traffic increases, the active CSMA period is accordingly extended by adding dynamic TDMA slots, allowing thus to efficiently handle burst traffic under real-time constraints. This protocol is implemented on the STM32W108 SOC chips and compared with both a fixed duty-cycle reference protocol and an optimized IEEE802.15.4 MAC protocol. Through extensive experimental measurements, we showed that our queue-length aware hybrid CSMA/TDMA MAC protocol largely outperforms the compared protocols. The proposed protocol can be easily implemented through slight adaptation of the IEEE802.15.4 standard. It presents an optimal bandwidth and energy allocation scheme according to the traffic to be carried. In fact, low-duty cycle, so low power consumption is preserved during light traffic load period, while high throughput is obtained during heavy burst load period.