###### Abstract  
The isometric mid-though pull (IMTP) is a reliable method to assess lower limb isometric muscle strength. A portable device (FysioMeter C-station) could serve as a suitable alternative. The reliability and concurrent validity of the FysioMeter C-station have not been evaluated for the IMTP unilateral test. The aims of this study were to (1) examine the between-session reliability of the unilateral IMTP test for the left and the right legs using the C-station, and (2) explore the concurrent validity of these measures when compared to gold standard force plates (AMTI). Twenty healthy, recreationally active males (age: 23 \(\pm\) 4 years, height: 1.81 \(\pm\) 0.60 m, weight: 79.6 \(\pm\) 10.8 kg) participated and completed test sessions one week apart. The participants performed the following: (i) three bilateral IMTPs on dual force plates (AMTIBI); (ii) three unilateral IMTPs on each leg on a single force plate (AMTIBI), AMTLIEFT); and (iii) three unilateral IMTPs on each leg on the C-station (CSRIGHT, CSLEFT). The peak force was measured in all the testing modalities and an Intraclass Correlation Coefficient (ICC) and Pearson Correlation Coefficient (PCC) were used to evaluate the reliability and validity. The C-station showed good between-session reliability for CSLEFT (ICC = 0.84) and CSRIGHT (ICC = 0.85). A strong concurrent validity (PCC \(\geq\) 0.82) was found for the C-station compared to the gold standard (AMTI). The C-station appears to be reliable for measuring unilateral IMTP in recreationally active males. Furthermore, strong concurrent validity of the C-station compared to the gold standard was demonstrated. I +
Footnote †: journal: applied sciences  
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Footnote †: journal: applied sciences  
a moderate to high correlation between the performance in IMTP tests and dynamic movements such as vertical jumping, short sprints, and change of direction [4]. IMTP tests have also been used in athletes in both unilateral and bilateral conditions, with unilateral IMTPs often used to evaluate strength imbalances between the lower limbs [4,5]. Additionally, isometric testing offers a quicker and potentially less fatiguing alternative to traditional one-repetition maximum (1 RM) testing [6]. Most previous studies have used force plates to measure the force production during an IMTP, which is considered the gold standard. The relative reliability in these studies for within-session intraclass correlation coefficient (ICC) ranged from 0.97 to 0.99, and for between-session ICC, it ranged from 0.95 to 0.97 [4,7,8]. In addition, some studies used weightlifting straps to reduce the impact of handgrip strength as a limiting factor in the IMTP [6,9,10]. However, the traditional force plates can be expensive, hard to transport, and difficult to operate [11]. Cheaper alternatives to the force plates, such as strain gauges, exist, but a novel device called the C-station has recently been developed to evaluate lower limb isometric strength [12], reaction time [13] and balance [14]. The C-station (FysioMeter, Aalborg, Denmark) is cheaper and easy to operate compared to traditional force plates. Pilot observations suggest the C-station can measure unilateral IMTP, and the device is highly portable, as it fits into a standard trolley (55 cm \(\times\) 40 cm \(\times\) 25 cm). The C-station uses a Nintendo Wii balance board (WBB) (Nintendo, Kyoto, Japan) and simple intuitive software to measure force. These advantages may allow sports teams to conduct more in-season monitoring of athletes. However, the reliability and validity of a unilateral IMTP performed on the C-station is unknown.