## 3 Results  
As shown in Figure 1, after evaluating 855 identified studies, 766 were excluded due to title or abstract (\(n=732\)) and duplicity (\(n=34\)) during the search. The remaining 89 studies were examined in full text, of which 19 articles fulfilled the inclusion criteria. Of the documents included in the systematic review, as shown in Table 1, four studies (21.05%) examined the effect of training in hypoxia on strength, three (15.78%) on hypertrophy and 12 (63.15%) analysed the training effect on both parameters. Additionally, 527 participants were included, ranging between 12 and 59 participants per study. Of the total participants, 92 (17.45%) were involved in studies investigating the effectiveness of resistance training under hypoxic conditions on muscle strength, 101 (19.16%) were part of protocols identifying the effect on muscle hypertrophy and a total of 327 (62.04%) on both strength and hypertrophy parameters [6, 10, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. Only two (10.53%) studies [26, 27] selected a female population to determine the effect of hypoxia on strength and hypertrophy. Additionally, two (10.53%) [15, 25] investigated the effect of hypoxia on the elderly population. Participants reported an average age of 27.37 \(\pm\) 30.22 years (elderly included) and an average weight of 71.45 \(\pm\) 3.25 kg. The papers included healthy participants (\(n=188\), 35.67%) [15, 16, 19, 21, 25, 28], trained or athletes (\(n=183\), 34.72%) [6, 22, 24, 27, 29, 30, 31] and a sedentary or untrained population (\(n=156\), 29.60%) [17, 18, 20, 23, 26, 32]. The studies analysed the effect of resistance exercise in hypoxia with a frequency of two to four times per week during 4 to 12 weeks, with a total of ten to 36 sessions. The training sessions consisted of two to six series and three to 30 repetitions. Only four studies used muscle failure methods during intervention sessions [19, 20, 27, 32]. Six documents (31.57%) based their prescribed load on 1 RM percentages less than 50% [16, 17, 18, 25, 27, 32]. On the other hand, two articles (10.59%) used loads higher than 80% of the 1 RM [21, 24], one (5.26%) [26] used maximal power as the reference value, and the remaining ten studies (52.63%) used a training load between 50 and 80% of 1 RM [6, 15, 19, 20, 22, 23, 28, 29, 30, 31]. Ten documents (52.63%) used lower limb exercises exclusively [16, 17, 18, 22, 26, 27, 28, 30, 31, 32], two papers (10.52%) focused on the upper limb [19, 23], and seven articles (36.84%) combined lower and upper limb exercises [6, 15, 20, 21, 24, 25, 29]. In Figure 4a,b, the 19 papers showed improvements in the percentage of change in at least one of the two groups. Of 15 documents that measured the hypertrophy variable, only three presented significant improvements in the control group [6, 17, 18], while the remaining 12 [15, 19, 24, 25, 26, 27, 28, 29] showed a greater percentage of change in the hypertrophy group concerning measurements 1 and 2 (Figure 4a). Figure 3: Evolution of published documents related to hypoxia in strength and hypertrophy variables in recent years. Figure 4: Percentages of change in hypertrophy (**a**) and strength (**b**) before and after training by group. * Significant difference. Sixteen documents measured the muscle strength variable, and only two showed significant improvements in the control group; two studies had an increase in the percentage of change but without differences between the groups, while the remaining 12 [15; 16; 17; 18; 20; 22; 23; 24; 28; 30; 31; 32] showed a higher percentage of change in the hypoxia group for the force variable concerning measurement 1 and 2 (Figure 4b). Moreover, 57.89% (\(n=11\)) report significant differences between the groups [6; 16; 18; 23; 26; 29; 32]. Considering the muscle hypertrophy variable, four documents presented a percentage of change between 5 and 10% between groups [22; 23; 25; 26], four manuscripts presented change percentages between 2 and 4.9% [19; 24; 27; 29] and seven studies under 2% [6; 15; 17; 18; 20; 21; 28].