# Assessment of Musculoskeletalelal Loads among Office Workers Due to Predicted BMI Increase
## 3 Results  
Based on the developed BMI prediction model, the average BMI values for Poland, Europe, and the world were determined for the period from 1975 to 2015, along with projected changes for 2020 to 2050. The predicted BMI values for the near future are presented in Figure 2.  
Figure 3 shows changes in the resultant reaction force values at joint L5-S1 in the lumbar section of the spine during standing and sitting down. The findings indicate that over the years and with increasing mean BMI values, the predicted loads on the lower spine would be greater. For the activities analyzed, the load differences between 1975 and 2015 were approximately 9-11% (65-70 N) while standing and 5-7% (97-115 N) while sitting down. The projected BMI increases suggest further increases in the resultant reaction force at L5-S1 by approximately 21-39% (135-271 N) while standing and 12-23% (204-401 N) while sitting down by 2050 compared to 1975 data. In addition, a consideration of individual components of the reaction force (i.e., compression and shear forces) at segment L5-S1 revealed variations between these daily activities. The compression force while standing ranged from 680 to 947 N (Poland), 658 to 796 N (Europe), and 549 to 683 N (world) from 1975 to 2050 and during sitting down from 1763 to 2159 N (Poland), 1703 to 1908 N (Europe), and 1436 to 1639 N (world). The shear force values were 99-151 N (Poland), 95-121 N (Europe), and 78-102 N (World) while standing and 198-267 N (Poland), 191-221 N (Europe), and 159-187 N (World) while sitting down. Depending on the year and group analyzed, sitting down generated approximately 2.2-2.5 times higher loads on the lumbar spine compared to standing.  
Figure 2: Mean BMI values in Poland, Europe, and the world (1975–2015) [2; 25] with predicted changes for 2020–2050.  
Similar tendencies were observed for loads on the hip and knee joints (Figures 4 and 5). The resultant reaction forces in these joints were predicted to increase over the years and with increasing BMIs. In the hip joint, over 75 years, loads ranged from 523 to 739 N (Poland), 508 to 620 N (Europe), and 429 to 542 N (World) while standing and 1300-1655 N (Poland), 1255-1437 N (Europe), and 1052-1231 N (World) while sitting down. The knee joint showed the highest forces exceeding 2300 N, with standing forces ranging from 767 to 1105 N (Poland), 748 to 921 N (Europe), and 639 to 811 N (World) and sitting down forces from 1578 to 2345 N (Poland), 1526 to 1927 N (Europe), and 1251 to 1648 N (World). While analyzing the results in terms of division into regions, the highest increase in loads was observed among Polish men, linked to the significant increase in BMI observed in recent years [2; 25].  
The analysis also considered the impact of BMI growth on muscle fatigue (Figure 6). The comparison of muscle activity recorded during everyday activities in 1975, such as standing and sitting down, revealed the following differences in the objective function values: 1.30 for the average Polish man, 1.22 for the average European, and 0.90 for the average male. The BMI growth observed until 2015, with predictions of further increases, suggests increased muscle fatigue by 2050. Differences in objective function values between analyzed activities are predicted to reach 2.86 for the average Polish man, 1.70 for the average European, and 1.20 for the average male in 2050. These growing differences indicate that the muscular system will need to generate greater force to perform the same activities. The simulation results suggested a potential 1.4-fold to 4-fold increase in muscle fatigue over these 75 years during both standing and sitting down activities.  
The obtained results were included in the Supplement Data S1.  
Figure 3: Predicted load changes in the L5–S1 segment (1975–2050): (**a**) resultant force, (**b**) resultant force normalized to 2015, (**c**) compression force, and (**d**) shear force while standing and sitting down. A red rectangle indicates the last year based on literature data.