## 4 Discussion
### Between-Session Reliability  
The absolute maximum torque values obtained by the H-station in the present study were very similar to findings of studies investigating a similar population [24; 26; 29]. Several studies have investigated the reliability of a handheld dynamometer (HHD) in relation to quadriceps and hamstring strength, but only a few have expressed the absolute values in Nm. Instead, most of the studies have used kg or N to express their absolute values obtained by HHD, which makes it difficult to compare the results obtained by the current study.  
In the current study, the H-station was found to be highly reliable for measuring both maximum quadriceps and hamstring torque (ICC = 0.91 for both). Furthermore, the reliability of the H-station measuring H/Q ratio was good (ICC = 0.89). One systematic bias was found between the mean of session 1 (138.2 Nm) and session 2 (149.6 Nm) for the Ham-H test, which could indicate a learning effect of the test [30]. Only one study has previously evaluated the reliability of the Nintendo Wii balance boards (WBB) for measuring lower limb strength in older adults [25]. This previous study found very similar reliability values compared to the current study, with ICC values for WBB ranging from 0.91 to 0.97, SEM from 9.7 to 13.9% and LOA ranging from 20.3 to 28.7%. Other portable strength measuring devices, such as HHD's, have shown ICC values between 0.86 and 0.96, SEM/CV between 4.2 and 14.7% and LOA (%)/MDC between 11.6 and 24.9% [17; 18; 29; 31]. For the isometric hamstring strength, previous studies found ICC's between 0.89 and 0.96, SEM/CV between 4.8 and 8.6% and LOA/MDC between 13.3 and 23.8 [17; 29]. Our results for both relative and absolute reliability were within the same ranges One study has evaluated the HHD's ability to measure H/Q ratio [29]. This latter study found ICC values ranging from 0.87 to 0.90, which corresponds to our study's ICC (ICC = 0.89) for H/Q ratio of the H-station.  
The SEM values reported here represent variation in torque due to three overall factors: instrumental-, biological- and/or experimental protocol variations [30]. Instrumental variation refers to the error or noise in the measuring equipment used. In relation to measuring error, one study has found excellent correlations (ICC = 0.83-0.99) of WBB compared to a laboratory-based force plate measuring force during a dynamic task [32]. This finding implies that the WBB is a reliable tool for measuring force in dynamic tasks, but it does not eliminate the possibility of variation due to signal noise or calibration errors. When testing human performance, random variations are usually caused by biological- and experimental protocol differences [25; 30]. Among biological factors, changes in mental and physical states between session 1 and 2 can account for some of the random variation [13]. The mental state was attempted controlled by providing verbal encouragement and visual bio feedback, which are suggested to have a positive influence on participants' physical performance [27]. It was not possible to control completely the participants' physical state, thus it is possible that the biological variations could account for the relatively high between subject variance in the data.