Many studies have compared quantitative profiles of the quadriceps femoris across different types of athletes as well as between athletes and untrained controls. In the 1980s, a number of studies measured quadriceps femoris size in athletes, such as sprinters, marathon runners (Johansson et al. 1987; Maughan et al. 1983), and bodybuilders (Schantz et al. 1983). Tsunoda et al. (1986) was the first to report quadriceps femoris size in several kinds of sports and compared them to those of untrained controls. They measured the ACSA of the quadriceps femoris at mid-thigh by using ultrasonography on 89 male Japanese elite athletes and 14 untrained men. In their results, the greatest ACSA was observed in sumo wrestlers, while those of sprinters and long distance runners were similar to those of untrained controls. This study indicates that all competitive sport athletes do not have hypertrophied quadriceps femoris. In addition, they also reported the relative ACSA for each muscle to the total quadriceps femoris ACSA. Their data clearly demonstrated event-related profiles for each muscle: for example, the percentage of the rectus femoris to the total quadriceps femoris ACSA was higher in the soccer players than in the volleyball players, long distance runners, oarsmen, and untrained individuals. However, they reported the ACSA only at one region (mid-thigh level); hence possible differences in hypertrophy among the four muscles at different regions was not taken into account.

In addition to ultrasonography, after the 1990s, MR imaging was introduced to evaluate the ACSA in many studies. This advance added a large field of view and high resolution. Some showed the difference of the quadriceps femoris size among the performance levels (Akima et al. 1992; Kubo et al. 2010) and among positions in the same sport (Kanda et al. 2013). For example, Akima et al. (1992) compared the ACSA of the quadriceps femoris at three (proximal, middle, distal) thigh levels for different levels of competitive play. The clearest results were for the comparison between the Japan national team players, a very elite group, and the Japan professional league players, a less elite group. The anatomical measurements indicated that at all three levels of the quadriceps femoris, the ACSA was larger for the Japan national team players. This study suggests that one of the important factors for good performance in competitive soccer is the size of the quadriceps femoris, although the underlying mechanisms for the greater ACSA in the Japan national team players remain unclear. On the other hand, Kano et al. (1997) failed to show a relationship between the ACSA of the quadriceps femoris and 100 m sprint time, suggesting that at least for sprinters, an increase in the ACSA of the quadriceps femoris does not lead to an improvement in sprint performance. Recent studies have supported this result (Hoshikawa et al. 2006b; Sugisaki et al. 2011). However, some studies did show a greater muscle thickness of the vastus lateralis (Abe et al. 2000, 2001) and vastus medialis (Ikebukuro et al. 2011) in sprinters as compared to untrained controls, with a significant association between sprint time and muscle thickness of the vastus medialis and vastus intermedius relative to body mass^1/3 (Ikebukuro et al. 2011). Therefore, no consensus has been reached regarding whether sprinters have an overall hypertrophied quadriceps femoris as compared to untrained controls.

Details of the muscular profiles in cyclists are also controversial. Hug et al. (2006) showed a greater ACSA of the quadriceps femoris in professional road cyclists as compared to recreationally active students. On the other hand, Izquierdo et al. (2004) reported a similar ACSA of the quadriceps femoris in comparisons between top level amateur road cyclists and untrained controls. The reasons for the inconsistency between these studies are unclear, but both studies measured ACSA of the total quadriceps femoris at one region. However, the ACSA of the total quadriceps femoris at one region does not represent the precise muscle volume for the entire muscle (Morse et al. 2007), and hence a similar evaluation may not have been done in both studies.

One of the athletic events in which athletes have remarkably hypertrophied quadriceps femoris is weightlifting (Ikebukuro et al. 2011; Izquierdo et al. 2004; Kanehisa et al. 1998a, b; Funato et al. 2000). For example, Kanehisa et al. (1998b) showed that Olympic weightlifters had greater (about 50 %) ACSA of the total quadriceps femoris than those of untrained controls. Moreover, recent investigation suggested uneven hypertrophy among the four muscles of the quadriceps femoris in weightlifters (Ikebukuro et al. 2011). The weightlifters had a greater muscle thickness in the vastus lateralis, vastus medialis and vastus intermedius as compared to those of untrained controls, but that of the rectus femoris was similar between the two groups. Competitive weight lifting mainly consists of explosive leg extensions (simultaneous extensions of knee and hip joints). Therefore, it can be assumed that the quantitative profile in weightlifters was due to leg extension exercises in their competitive and training activities. In a recent study we examined quantitative muscle profiles in oarsmen and the data supported this idea (Ema et al. 2014). We compared the muscle volume of the individual muscles of the quadriceps femoris between experienced oarsmen and untrained controls. It was shown that experienced oarsmen had about a 30 % greater volume of the vastus lateralis, vastus medialis, vastus intermedius, but rectus femoris volume was similar between the two groups. In addition to our cross-sectional studies, previous functional studies (Chin et al. 2011; Escamilla et al. 1998, 2001) also supported the above results. For example, Escamilla et al. (1998) determined muscle activation level during squat and leg press exercises using electromyography. The results indicated that the activity level in the vastus lateralis and vastus medialis was 30–90 % greater than that in the rectus femoris. It was recently shown that differences in muscle activation over synergistic muscles during resistance training was associated with the differences in the magnitude of muscle hypertrophy (Wakahara et al. 2012). Given the above studies, it is likely that differences in muscle activation during leg extension may lead to the quantitative profiles of the quadriceps femoris in weightlifters. However, the underlying mechanisms for the difference in muscle activation among the four muscles during leg extension is not clear.