This study analyzed growth hormone levels throughout two different training sessions and found that subjects using forced reps had a higher growth hormone response during the training session. Use this method by having a spotter help you force out 2-3 extra reps per set after you reach failure.
Source: Ahtiainen, J. P., Pakarinen, A., Kraemer, W. J., & Häkkinen, K. (2003). Acute hormonal and neuromuscular responses and recovery to forced vs. maximum repetitions multiple resistance exercises. International Journal of Sports Medicine, 24(06), 410-418.