The current study examined the hand asymmetry of the thickness and strength of the FD and the strength of the ED between musicians and non-musicians aiming to assess possible occupational effects on the muscular characteristics of musicians.

With respect to hand asymmetry, several studies so far have reported that the dominant hand has about 10% greater handgrip strength in right-handed participants. [25,26,27]. As expected, in the present study, in which all participants were right-handed, the asymmetry ratio for muscular strength and thickness in the non-musician group indicated larger values for the dominant hand with 4.3%, 7.5% and 6.3% for the T-FD, the S-FD and the S-ED respectively. Interestingly, in musicians, the asymmetry was less pronounced, 1.1%, 5% and − 0.2% for the same assessments respectively (Fig. 2). The clear tendency for musicians toward 0% indicates a more equal distribution between dominant and non-dominant hands. The tendency for more equally-distributed strength and muscle thickness became even more evident after categorizing musicians into those who primarily use fingers of their left hand (e.g., violinists) and those who use fingers of both hands to a similar degree (e.g., pianists). Musicians who typically use fingers of both hands to play showed the same pattern as non-musicians. In contrast, the majority of musicians who extensively use fingers of their left hand revealed a clear tendency towards less asymmetry or even a non-dominant hand superiority for the thickness flexor assessment (Fig. 3). The largest non-dominant hand superiority was observed for this group of musicians in the strength extension assessment (S-ED). The large effect of the strength extension toward non-dominant superiority can be attributed to the fact that playing a musical instrument requires considerable extension of the fingers. Compared to finger flexion movements, extension movements are less common during everyday activities, which could also explain why no differences were observed in the strength flexion assessment.

Similar results were found for the percentage of musicians who exhibited larger asymmetry toward the non-dominant hand; this effect was much larger for the “left hand used” group as compared to the other two groups (“both hands used” and “non-musicians”). This effect was obvious for the T-FD and significant for the S-ED (Fig. 3). The S-FD indicated no important differences concerning the percentage distribution across the three different groups. In particular, the proportion of hand superiority for non-musicians was relatively constant for all the assessments (~ 5:1, right: left hand superiority). These proportions are comparable to Incel et al. [27] who found that during a pulp pinch measurement of the first and second digit across 121 right-handed individuals, only 28% of participants were stronger in the non-dominant hand (4:1, right: left hand superiority). In contrast, for musicians who mostly use their left hand while playing, these proportions indicate superiority towards the left, non-dominant hand. For instance, the proportion for the S-ED was ~ 1:6, right: left hand superiority and for the T-FD it was ~ 1.3:1, right: left hand superiority. Our results suggest that right-handed musicians who play instruments requiring extensive usage of the left-hand fingers (e.g., violin) could have smaller (or even inverse) muscular thickness and strength extension asymmetries between the two hands. In contrast, musicians who extensively use fingers of both hands, such as pianists, exhibit muscular asymmetries more similar to non-musicians.

Different bilateral asymmetries due to the impact of the different instruments were also observed in skill activities and neural plasticity. For instance, Jäncke et al. [1] found that musicians exhibited reduced hand skill asymmetry compared to non-musicians. The authors argued that the reduced right-hand superiority was mainly an effect of extensive usage of the left hand and not due to a reduced skill of the right hand. Also, Bangert et al. [13] reported that the precentral gyrus in the right hemisphere of violinists was enlarged while it was smaller in keyboard players. The authors suggested that such structural brain differences might reflect an adaptation to the specific instrumental demands.

Finally, a positive correlation was observed in non-musicians between T-FD and S-FD asymmetry. A similar finding was also reported in the study of Abe and Loenneke [25] that examined a group of 31 young women and found that forearm muscle size was positively correlated with handgrip strength dominance. Notably, there was no sign for correlation in musicians and there was no significant difference between the two correlation coefficients. One explanation is that muscular mass is only partly or non-linearly related to muscular strength [28]. For instance, it has been suggested that a possible increase in strength could be achieved without any morphological changes such as muscle size. The increased muscular strength might be an adaptation of the motor system [29,30,31]. Past studies have already showed that strength training in childhood can increase muscular strength due to neuromuscular adaptations without hypertrophic factors [30, 32]. This finding could probably explain why extensive finger movements or increased finger strength can result in macroscopic adaptations in the nervous system of musicians [13] without any evidence of morphological changes in muscle thickness.

Muscular symmetry between the hands generally offers more advantages than disadvantages, particularly in the context of injury prevention and recovery from peripheral or central injuries. After an injury, symmetrical muscle development can facilitate recovery. If both hands (and associated musculature) are strong and well-coordinated, the unaffected hand can better assist and support the injured one during the rehabilitation process. For peripheral injuries (such as those affecting the limbs), balanced musculature can help distribute the workload during rehabilitation, allowing for more effective and less painful recovery. In the case of central injuries (such as those resulting from a stroke or spinal cord injury), muscular symmetry may aid in recovery as well. Symmetrical muscle development can support neuroplasticity, where the brain reorganizes itself by forming new neural connections [33]. Bilateral training can be particularly effective, helping the brain to recover motor functions by using both sides of the body in training [34]. Individuals with symmetrical muscle strength may find it easier to perform activities of daily living, as both hands are equally capable of performing tasks, leading to quicker and more comprehensive recovery of functional independence. However, individuals who engage in activities that demand high levels of bilateral muscle use might increase the risk of simultaneous or successive injuries to both sides. This is less common compared to asymmetric overuse injuries. Additionally, in the event of an injury, individuals with symmetrical muscle development might unintentionally overcompensate with the uninjured side, potentially leading to overuse injuries if not managed properly. In general, muscular symmetry supports balanced strength and coordination, which can contribute to more efficient and effective motor function, beneficial in daily activities and sports. Symmetrical muscular development can reduce the risk of overuse injuries, as there is less strain on individual muscles and joints when one side of the body is not compensating for the other [35].

Future studies could recruit a larger number of musicians to examine further occupational differences not only from hand but also from facial muscles, for instance in wind players. In addition, a sample derived from a broader age range of musicians can provide us with information on when muscular asymmetry first becomes apparent, how it sustains over the years, and how it behaves in older ages where the hours of practice gradually decrease. Finally, an interesting approach would be to investigate differences between musicians and people from other occupations requiring extensive use of the fingers, such as typists. This will enhance our understanding on how small muscles either in the forearm or around the mouth adapt to the different occupational demands.