The US economy got a shot in the arm on Thursday from Q2 GDP figures just out showing a 4.2 rise, a better-than-expected figure.br Details also pointed to sustainable underlying strength.br br Business spending and exports exceeded forecasts, helping explain the rise. Domestic demand grew by 3.1 instead of the previously reported 2.8, suggesting that with a unusually cold winter that cut output over, the economy is making up for lost time.br br Gross domestic income also surged by 4.7, reflecting the strong jobs gains during the quarter.