Cycling race is a sprint competition in which seven players in the Velodrome run seven laps of 333.33-m raceway along the inductor and determine the ranking by the last two laps. The pedaling power that explodes in a short time is an important factor in determining the win or loss of the competition (Atkinson et al., 2007).

Pedaling power is the force applied repeatedly to the pedals by the extensor and flexor muscles of the hip, knee, and ankle (McDaniel et al., 2014). Among the muscle fibers in the lower limbs, pedaling power affected by the muscle type and volume of muscle fibers involved in the pedaling, and it is closely related to the coordination of the hip, knee, ankle and external oblique abdominal muscle (Elmer et al., 2011). In the previous studies, Baum and Li (2003) reported that maximum and average power in cyclists are highly correlated with maximum muscle strength around the knee and hip joint, and quadriceps strength, anaerobic power and maximum oxygen uptake are crucial physical fitness to win the competition (Sakamoto et al., 2018).

In order to improve the pedaling power of cyclist, it is necessary to apply a systematic training program for effective interaction of core strength and upper and lower muscular strength that can maintain the body posture during cycling (Hartmann et al., 2015; Rønnestad and Hansen, 2018). The core stability exercise is a method of exercise that enhances the maximum strength of the back, thigh and hip muscles, suggesting that this increased maximum strength can improve the flexibility and balance as well as shorten cycling records to cyclists (Willson et al., 2005). According to various studies that reported a relationship between performance and core strength in elite athletes, core exercise increased maximum strength of hip flexor muscles and range of motion of hip joint (Hodges, 2003). Also in the study related to cycling performance, the increase of isokinetic lumbar muscle strength in men and women cyclists was associated with the game record (Drust et al., 2005).

In addition to core strength, basic physical fitness of upper and lower body is another factor in deciding whether to win the cycle competition (Mujika et al., 2016; Rønnestad et al., 2016). One-repetition maximum (1RM) of bench press, squat, hand-grip and back strength have been used for measuring basic physical fitness of cyclists. Particularly, hand-grip and back strength are important fitness factors to hold steady handles and transmit power to cycle, and it has been known that two factors have a high correlation with the game record (Faria et al., 2005; Hansen et al., 2007).

With these results mentioned by previous studies, maximum muscle strength of core and upper and lower body is essential for increasing performance of amateur cyclist. However, a study on the variety of fitness factors related to the performance that affects the pedaling power of the top level racing cyclists is rare.

Therefore, the purpose of this study was to investigate differences of maximum muscle strength and isokinetic knee and core muscle functions according to pedaling power of racing cyclist candidate.

Wingate test has been known to be an appropriate devise for evaluating anaerobic capabilities of cyclists and this result is important information that predicts the pedaling power of cyclists (Craig and Norton, 2001). In Wingate test, PP (W or W/kg) means power for about 5 sec after peak pedaling, and it is closely related to fast speed up in the competition. AP and FI also is the ability to maintain the cadence for 30 sec after the start of the peak pedaling, predicting the performance at the end of the competition (Rønnestad et al., 2015). Thus, we think that the training program for improving the performance of racing cyclists should be composed of training to increase the pedaling power through up-regulating the contribution of anaerobic energy system.

In this study, PP of racing cyclist candidates after Wingate test were 1,033.9 W (12.1 W/kg) for TPP, 1,028.6 W (12.0 W/kg) for TAP, 745.3 W (9.1 W/kg) for LPP and 790.6 W (9.3 W/kg) for LAP, respectively. All PP values were higher in top 10% groups than in the lower 10% groups and there are significant differences between all groups. Korea Institute of Sport Science (KISS) analyzed the results of Wingate test on elite cyclists in 2008. They suggested that the A grade of PP was over 1,091.09 W, the B grade was over 959.63 and less than 1,091.09 W, the C grade was over 828.17 and less than 959.63 W and the D grade was over 696.71 and less than 828.17 W. PP in PPT and APT groups belongs to B grade, PP in PPL and APL groups was D grade, and there are differences between the upper 10% group and the lower 10% groups. AP of racing cyclist candidates were 789.9 W (9.3 W/kg) for TPP, 809.0 W (9.4 W/kg) for TAP, 607.5 W (7.4 W/kg) for LPP and 618.2 W (7.2 W/kg) for LAP, respectively. All AP values were higher in top 10% groups than in the lower 10% groups. In addition, AP measurement standard proposed by KISS is the A grade of over 800.58 W, B grade of over 734.04 and less than 800.58 W, C grade of over 661.5 and less than 731.04 W and D grade of over 591.96 and less than 661.50 W. The TAP group had a grade A, the TPP was a grade B, and LPP and LAP belong to D grade. FI showed no significant difference between groups. Previous studies reported Wingate test results for cyclists suggested that PP and AP improvements were necessary for a positive change in cycle performance (Rønnestad et al., 2015; Vikmoen et al., 2016). These findings were in agreement with the results of this study that maximum pedaling power training w applied to win the game.

Cyclists try to maintain their body fat percentage at 5%–9% through dietary restrictions and to increase muscle strength by anaerobic high intensity training (Lericollais et al., 2011). In the present study, %Fat in racing cyclists were 17% for TPP, 16% for TAP, 19.3% for LPP and 20.1% for LAP. The top 10% groups had lower percentage body fat as well as FFM was 71.1 kg for TPP, 72.2 kg for TAP, 66.3 for LPP and 67.7 kg for LAP. The top 10% groups were about 5 kg higher than low 10% groups. Haakonssen et al. (2016) represented that amateur cyclists have higher %Fat and BMI than elite cyclists and must be controlled to improve performance (Lee et al., 2002; Martin et al., 2001). In general, a cyclist with a low body weight, %Fat, and BMI can minimize the wind resistance that worsens the propulsive force, which can lead to a positive result in the competition (Craig and Norton, 2001).

In the present study, the results of 1RM squat and grip strength test and in racing cyclist candidates showed significant difference in absolute value of top 10% groups, but 1RM bench press did not show any significant between groups. These findings suggest that leg and grip strength are more relevant to the improvement of performance of cyclists than that of pectoralis major muscle. The present results are consistent with several previous studies that cyclists with excellent performance had higher maximum strength of quadriceps, hamstring and latissimus dorsi muscle (Hansen et al., 2007; Hodges, 2003).

Cycle pedaling produces in the movement of knee joint by strength of gluteus and hamstring muscles. Muscular activity in the gluteus and quadriceps muscle is high at the pedaling angle of 0°–180° and hamstring muscle activation increases at 181°–360° (Elmer et al., 2011; McDaniel et al., 2014). Willson et al. (2006) stated that isokinetic equipment is an important tool for measuring the maximum muscle functions of elite cyclists, and isokinetic evaluation index is necessary for predicting performance. In this study, isokinetic right knee flexor (P<0.013) and extensor (P< 0.001) strength, and left knee extensor (P<0.002) strength was significantly higher in the top 10% groups compared to the low 10% groups. Also isokinetic trunk flexor (P<0.003) and extensor (P<0.017) strength in the top 10% groups showed significantly higher values than those in the low 10% groups. The previous study reported the correlation between isokinetic knee and trunk functions and pedaling power (Howe et al., 2013), and van Soest and Casius (2000) increased the reliability of our results.

In conclusion, we think that the maximum strength and pedaling power training program should be applied to improve the performance of the racing cyclist candidates and extend the life of the athletes. Therefore, our findings provide important evidence that maximal strength of upper and lower limbs and isokinetic knee and core muscle functions are predictors of the pedaling power in racing cyclist candidates.