The experimental protocol involved five visits to the University of Essex biomechanics lab. The first enabled subjects to become familiar with the data collection procedures and allowed the assessment of descriptive statistics. The thickness of adipose tissue overlaying the quadriceps muscle was measured using a skinfold caliper (British Indicators, Harpenden, UK) and maximal voluntary contraction (MVC) of the knee extensors was measured with a dynamometer (KinCom, Chattex; Chattanooga, TN). All subjects performed a nonspecific light warm up on a cycle ergometer (Monark, 824E). Subjects were securely attached to isokinetic dynamometer using both a waist and upper body strapping attachment to minimize any upper body contribution to the quadriceps contraction. The dominant leg was then selected and fixed at a 60 deg angle and three repetitions of a 5 s continuous maximal isometric contraction with a 60-s rest period were performed. The strongest contraction of the three repetitions was then taken as the maximal isometric force. Values for 10%, 30%, and 50% MVC were then calculated. On the second and third visits the subject was required to perform a series of 30 s sustained isometric quadriceps contractions to the previously defined values of their MVC followed by a 3-min period of rest; at 10% of MVC, 30% MVC, and finally at 50% MVC. During the second and third visits, the PortaMon device was positioned on the belly of the vastus lateralis muscle, midway between the greater trochanter of the femur and the lateral femoral epicondyle. To ensure the optodes and detector remained in position relative to the subject’s skin, the device was fixed into position using tape and secured with a black neoprene strap. During the fourth and fifth visits to the lab, the same protocol was repeated but with the PortaMon device encased in the previously designed waterproof casing. To ensure accuracy of repeat device placement, an outline of the device was drawn onto each subject’s leg. Subjects were asked to maintain the outline during the testing period. Additionally, any bodily hair within the probe placement area was removed from each subject’s skin and subjects were asked not to use any moisturizing products on the testing day. The same researcher attached each device and applied the sports strapping, asking the subjects if the device and strapping felt comfortable and secure. All visits were at intervals of between 3 and 5 days and testing was performed at the same time of day.