This is the first investigation on an elite powerlifter to analyze single muscle fiber MHC isoform distribution, fiber size, and myonuclear content. Our participant demonstrated an extreme preponderance of MHC IIa fibers, and while these fibers ultimately displayed a fairly typical size, their MND was relatively small. Unsurprisingly, the EPL had few hybrids and a substantial expression of the MHC IIa isoforms. The EPL’s MHC IIa content is comparable to the highest known MHC IIa content to date, recently recorded by our research team in world-class weightlifters (79% vs. 71%, respectively) [38]. His extensive training age and almost 80% MHC IIa proportion matches previous work in powerlifters, weightlifters, and anaerobically trained athletes that describes a fast-twitch shift [10, 12, 13, 16, 22, 32, 38]. The relationship between training exposure and MHC IIa content is further corroborated by Serrano et al. [38], who described a higher MHC IIa percentage in world-class female weightlifters (WCF) of greater training age relative to less experienced national-class female (NCF) weightlifters. It should be noted that four individual weightlifters (3 WCF and 1 national-class male [NCM]) had a greater proportion of MHC IIa fibers and comparable levels of MHC I fibers to EPL. Nevertheless, our participant has a higher MHC IIa content compared to the majority of world-class male and female weightlifters, achieving this distribution at a much older biological age (40 years [EPL] vs. 23.6 ± 3.9 [NCF] and 25.6 ± 3.8 years [NCM]) [38]. The ability to maintain a fiber type profile at the EPL’s age is unprecedented in the current literature, and it can be assumed that is possible through the synergistic effects of HRT and AAS administration [10]. Along with a higher MHC IIa content, the EPL has a higher percentage of I/IIa hybrid fibers similar to previously investigated bodybuilders [21]. This is likely due to the EPL’s focus over the previous 3 years on bodybuilding-style training. Conversely, the current investigation did show a stark contrast to Kesidis et al. [21], where the average percent distribution of MHC IIa fibers was 30% in student controls and 38.8% in bodybuilders, compared to a daunting 79% in EPL. Furthermore, the mean distribution of MHC I expressing fibers was 40.3%, 35.1%, and only 9% in student controls, bodybuilders, and EPL, respectively. Across various athletic demographics analyzed via single fiber SDS-PAGE, it is extremely uncommon to have an MHC I content below 10% in the human vastus lateralis. Nevertheless, the results support the findings of Kadi et al. [19], who observed significantly lower MHC I content in powerlifters compared to sedentary controls. It can be hypothesized that perhaps the culmination of training frequency, training volume, as well as factors related to AAS exposure history and dosing patterns are responsible for the EPL’s differential fiber type profile.

The mean CSA of the EPL’s MHC IIa fibers was higher than sedentary populations and older track athletes in previous research, but not noticeably higher than an elite sprinter or younger track athletes [23, 36, 41]. Previous work by Eriksson et al. [10] showed that elite-level powerlifters using AAS had a higher CSA in type II fibers compared to drug-naïve controls. This does not appear to be the case in the EPL, regardless of his extensive AAS use. This discrepancy may be due to the small sample size inherent to a case study approach or to exclusion of data outliers. Specifically, one fiber was omitted from data analysis due to a cellular volume that was more than two standard deviations higher (3,833,006 μm3) than the mean. Mention of this outlier should not be overlooked from the current discussion because it did fit sarcomere length criteria for analysis. Interestingly, this fiber is more than 22% greater than the average CSA of Rhinoceros MHC IIa fibers seen in an investigation by Liu et al. [24] (see Fig. 2b).

This is the first determination of MND size in an elite powerlifter, also utilizing single fiber SDS-PAGE methodology (see Table 1). Due to lacking MHC isoform expression diversity, MND in the EPL could only be determined in MHC IIa fibers. One MHC IIa fiber was excluded from analysis due to a myonuclear number that was > 2 × standard deviations from the mean value (458 myonuclei/mm vs. mean 170 ± 30 myonuclei/mm). Compared to earlier work using similar myonuclear determination methods, the EPL had a lower MHC IIa MND relative to healthy men ranging from 21 to 96 years old (12,836 ± 4388 μm3 [EPL] vs. 35,100 ± 2500 μm3 [21–31-year-old men] and 23,500 ± 1400 μm3 [65–96-year-old men]) (see Fig. 2c) [5]. Another investigation examined a human male subject with a MND of 32,900 ± 2100 μm3, ultimately greater than our findings in EPL [24]. Our participant’s chronic HRT experience may consequently impose a smaller MHC IIa MND to meet protein turnover demands and subsequent recovery [35].

Table 1 List of studies that include skeletal muscle fiber type-specific myonuclear domain (MND) size measures via confocal microscopy in human subjects (i.e., similar methods as the current case study) [5, 24, 28, 31, 36] Full size table

Unfortunately, the 50 fibers from the EPL that were imaged did not yield sufficient MHC I fibers for comparison to MHC IIa. As previously mentioned, type I fibers are preferentially affected acutely in response to muscular stimuli (or lack thereof) and aging [14, 20]. Multiple investigations have found a smaller slow-twitch MND due to increased demand for cellular turnover [35]. Furthermore, it would have been illustrative to determine how the EPL’s fiber type-specific MND correlated with both his age and training status. Work by Cristea et al. [5] described an increased MHC I MND and decreased MHC IIa MND with increasing age. Nevertheless, comparing the singular MHC I fiber that was available, the results corroborate a smaller MHC I MND in prior literature [35].

One unique characteristic to our case subject was his extensive AAS use, which has been shown to cause differential effects on MND size. The EPL’s lower MHC IIa MND size compared to male participants in previous investigations is supported by Kadi et al. [19] and Eriksson et al. [10]. Their work determined AAS-using powerlifters had a higher myonuclear number per cell volume. Conversely, Yu et al. [44] saw no difference in myonuclear density when accounting for fiber size, but the difference may be due to a discrepancy in MND determination methodology, in which the latter investigator utilized immunohistochemistry (i.e., cross sections). Moreover, the subjects were not homogenously powerlifters, but rather were a mix of bodybuilders, weightlifters, and strongmen [44]. It is also worth noting that the EPL has had a historically inconsistent AAS dose and usage pattern. The current investigation can only confirm the EPL’s anecdotal dosage and pattern of AAS use from the last 4 years under medical supervision; however, he had professed to haphazard experimentation with varying doses and combinations of performance enhancing substances since around age 25. Nevertheless, rodent models have shown AAS use can cause higher myonuclear retention and a greater sensitivity to training after drug cessation [8]. This gives credence to speculate the augmentative effects of years of varying AAS compounds and their ability to endure and compound across multiple years.

Very few investigations in human performance-centered AAS administration report substance dose or use patterns [4, 10, 17, 18]. The highest reported dose of 938 ± 527 mg/week testosterone was in a cross-sectional analysis of powerlifters [10]. This is comparable to the ≥ 500–600 mg/week regimen used over the last ~ 4 years by EPL. Regardless, both AAS patterns are confounded by undocumented, intermittent experimentations with cocktails of other illicit performance enhancing drugs, including IGF-1 and other testosterone derivatives [10]. The inability to hitherto control for past AAS use in athletic populations is an issue that is not easily resolved; safe, empirically backed use is undermined by social and moral barriers that stigmatize use for performance enhancement [15].