The aims of this thesis were to determine if whole muscle rate of torque development (RTD) and single fibre rate of force redevelopment (ktr) are lower in older adults compared to young adults, if ktr and RTD are associated with each other, and if ktr is affected by [Ca2+] in humans. Knee extensor muscle strength, speed, power, and RTD were lower in old compared to young. Single fibre ktr was not different between young and old. There were ktr-RTD relationships trending toward significance in older TI fibres. Human single fibre ktr was also affected by [Ca2+] such that with increasing [Ca2+] ktr increased. In old single fibres, calcium sensitivity (pCa50) was strongly associated with ktr, such that with increasing pCa50, ktr increased. This work has confirmed the ktr-[Ca2+] relationship in humans and found an emerging relationship between ktr and RTD in older adults.