The average age of the entire cohort (N = 71, Table 1) at the time of examination was 63.2 years (standard deviation, SD, 12 years) with an age of onset of 61.5 years (SD 12.4 years). The female/male ratio was 45:55% in the entire cohort, bulbar onset was observed in 20 individuals, whereas spinal onset was observed in 46 cases. Two out of 71 had a positive family history of ALS. BMI at onset was 25.9 (SD 3.45), whereas at the time of examination, it was 24.7 (SD 3.3). The mean Amyotrophic Lateral Sclerosis Functional Rating Scale (ALS/FRS) score at the time of testing was 41.3 (SD 3.83).

n = 38 patients, including 17 males and 21 females with a mean age of 66.5 years (SD 8.75), displayed no paresis in the biceps, triceps brachii, or deltoid muscle (Table 1). Seventeen patients reported spinal onset of disease, 17 bulbar, three thoracic onsets, and in one patient the site of onset remained uncertain retrospectively. No patients showed a positive family history. In this group, the patient's BMI decreased on average by 5% following disease onset.

n = 33 patients, including individuals displaying at least weakness in one muscle of the six target muscles (BMRC < 5) (Table 1), had a somewhat earlier age of onset (57.8 years, SD 14.1) than the previous group. They were also younger at the time of examination. Both differences were statistically significant (p = 0.019 and p = 0.012; Chi-square-test).

Not surprisingly, we saw more patients with a spinal onset in the second group (n = 29), whereas only three had bulbar onset. In this group, we saw two patients with a positive family history; loss of BMI after disease onset was 4%. The ALS/FRS scores of both groups were comparable (41.7 versus 40.8; p = 0.46, t-test).

No statistical differences between right and left muscle groups were found for each comparison (biceps: p = 0.32; triceps: p = 1.00; deltoid: p = 0.83). Therefore, we grouped the muscles irrespective of the side examined.

In the first step, we compared the muscle strength (MRC scores) of all muscle groups, including those with an MRC score of 5 in all muscles (no paresis). In all MRC scores, we did not see a normal distribution (Sharpino–Wilk test). Therefore, the Wilcoxon test was used to identify significant differences and Spearman’s test was used to find correlations. The MRC scores of the biceps and the triceps brachii were significantly different (p < 0.001). The same was true for the comparison of the deltoid muscle and the triceps brachii (significant difference with a p value < 0.001) (Fig. 2). By contrast, the differences between the paresis scores for the deltoid and biceps brachii (Fig. 3) were not different (p = 0.16), but also showed a significant positive correlation (R = 0.84, p < 0.001).

The BMRC Score of the lateral deltoid is compared with elbow extension (triceps brachii) in N = 71 patients. In 26.8% of patients, the triceps was stronger than the deltoid, in 73.2% we found no difference, and in no individual was the triceps stronger than the deltoid. The difference attained statistical significance (p < 0.01)

The BMRC Score of the lateral deltoid compared with elbow flexion (biceps brachii) in N = 71 patients. In 81.7% of patients, both muscles developed the same strength on the BMRC scale, in 9.8% the biceps was weaker, and in 8.4% the deltoid was weaker. The difference was not statistically significant (p = 1.00)

In the second step, we analyzed the scores of those patients who had at least one paretic muscle (MRC < 5; n = 33). In summary, we obtained identical results, even in the smaller group, displaying paresis; there was no statistically significant difference between deltoid and biceps (p = 0.16) with a positive correlation (R = 0.83, p < 0.001), but a statistically significant difference between the triceps and biceps (p < 0.001) and between the triceps and deltoid muscles (p < 0.001).