The training adherence was 99% ± 2% in both the E+S and S+E training groups. All subjects completed at least 90% of the overall training volume.
The analysis of reliability revealed an ICC >0.7 for all test measures, indicating high reproducibility. The ICC of endurance and strength performance, body composition, and blood lipid measures were 0.737–0.955, 0.786–0.975, and 0.763–0.866, respectively.
Total energy intake at weeks 0, 12, and 24 were 9.3 ± 1.8 MJ, 10.2 ± 2.6 MJ, and 9.5 ± 2.6 MJ in E+S and 9.4 ± 2.0 MJ, 9.3 ± 1.7 MJ, and 7.9 ± 1.7 MJ in S+E. The average nutritional intake as percentage of total energy for CHO, fat, and protein were 42%–45%, 31%–36%, and 17%–19% in E+S and 42%–44%, 33%–36%, and 18% in S+E throughout the 24 wk of training. No significant within- or between-group differences were observed.
Absolute values of physical fitness at weeks 0 and 24 are presented in Table 1. Significant main effects for time were observed in 1RM (F = 73, P < 0.001), MVCmax (F = 14, P < 0.001) and MVC500 (F = 15, P < 0.001). Both groups significantly improved 1RM strength (Fig. 1) at weeks 12 (E+S, 9% ± 8%, P < 0.001, ES = 0.456; S+E, 12% ± 8%, P < 0.001, ES = 0.772) and 24 (E+S, 12% ± 9%, P = 0.001, ES = 0.620; S+E, 17% ± 12%, P < 0.001, ES = 1.032). The increase from week 12 to week 24 was significant in both groups (P < 0.05). Similarly, MVCmax significantly increased in both groups at weeks 12 (E+S, 10% ± 10%, P = 0.010, ES = 0.345; S+E, 9% ± 12%, P = 0.019, ES = 0.337) and 24 (E+S, 10% ± 12%, P = 0.025, ES = 0.302; S+E, 13% ± 18%, P = 0.024, ES = 0.482), whereas MVC500 increased significantly in S+E only at weeks 12 (13% ± 15%, P = 0.002, ES = 0.623) and 24 (14% ± 18%, P = 0.005; ES = 0.620).
Significant main effects for time were observed in time to exhaustion (F = 83, P < 0.001), maximal aerobic power (F = 71, P < 0.001), and V˙O2max (F = 12, P < 0.001). Both groups significantly improved time to exhaustion (Fig. 2a) at weeks 12 (E+S, 9% ± 9%, P = 0.003, ES = 0.387; S+E, 10% ± 6%, P < 0.001, ES = 0.551) and 24 (E+S, 15% ± 9%, P < 0.001, ES = 0.859; S+E, 17% ± 7%, P < 0.001, ES = 1.027) and maximal aerobic power (Fig. 2b) at weeks 12 (E+S, 8% ± 9%, P = 0.011, ES = 0.820; S+E, 9% ± 7%, P < 0.001, ES = 0.630) and 24 (E+S, 13% ± 9%, P < 0.001, ES = 0.830; S+E, 16% ± 7%, P < 0.001, ES = 1.074). The increases in aerobic power in both groups from week 12 to week 24 were significant (P < 0.01–0.001). The observed increases in V˙O2max were significant at both weeks 12 (E+S, 4.8% ± 7%, P = 0.051, ES = 0.266; S+E, 7.3% ± 8%, P = 0.003, ES = 0.339) and 24 (E+S, 6.1% ± 8%, P = 0.041, ES = 0.366; S+E, 6.4% ± 12%, P = 0.006, ES = 0.396). No significant between-group differences were obtained for the measures of physical fitness.
Absolute values of body composition measures at weeks 0 and 24 are presented in Table 1. A significant increase in body weight and BMI was observed in S+E only (1.7% ± 2.4% and 1.7% ± 2.6% at weeks 12 and 24, respectively, P < 0.05). No significant changes in body fat percentage, total fat mass, or abdominal fat mass were observed in the two groups at either week 12 or week 24. A significant main effect for time was observed for muscle CSA at 30% (F = 18, P < 0.001), 50% (F = 50, P = 0.001), and 70% (F = 60, P < 0.001) of VL (Fig. 3). Both groups significantly improved average CSA of VL at weeks 12 (E+S, 8% ± 7%, P = 0.002, ES = 0.490; S+E, 9% ± 7%, P < 0.001, ES = 0.643) and 24 (E+S, 14% ± 7%, P = 0.001, ES = 0.822; S+E, 16% ± 8%, P < 0.001, ES = 1.178), whereby the increase from week 12 to week 24 was significant (both groups, P < 0.001).
A significant main effect for time was observed for total lean mass (F = 8, P = 0.001), upper body lean mass (F = 13, P < 0.001), and leg lean mass (F = 49, P = 0.001). Both groups significantly increased total lean mass (Fig. 4a) at weeks 12 (E+S, 2% ± 3%, P = 0.042, ES = 0.203; S+E, 3% ± 2%, P < 0.001, ES = 0.310) and 24 (E+S, 3% ± 3%, P = 0.001, ES = 0.329; S+E, 3% ± 2%, P = 0.001, ES = 0.342). Similarly, both groups increased upper body lean mass (Fig. 4b) at weeks 12 (significant in S+E only, 2% ± 3%, P = 0.022, ES = 0.212) and 24 (E+S, 3% ± 3% P = 0.005, ES = 0.253; S+E, 2% ± 3%, P = 0.025, ES = 0.218) and leg lean mass (Fig. 4c) both at weeks 12 (E+S, 2% ± 3%, P = 0.024, ES = 0.210; S+E, 3% ± 2%, P < 0.001, ES = 0.373) and 24 (E+S, 4% ± 3%, P < 0.001, ES = 0.361; S+E, 4% ± 2%, P < 0.001, ES = 0.427). The increase in leg lean mass from week 12 to week 24 was significant in E+S only (P < 0.05). No significant between-group differences for the measures of body composition were obtained.
Only minor changes in total cholesterol, HDL-C, LDL-C, and triglyceride levels were observed after 24 wk of training (Table 2). A significant between-group difference was observed for LDL-C levels at week 12 (P < 0.05) but was diminished after 24 wk of training.
Correlations of physical fitness and body composition across all experimental subjects
All absolute values of physical fitness at baseline (1RM, MVCmax, MVC500, aerobic power, time to exhaustion, and V˙O2max) were significantly correlated with the corresponding relative changes obtained at weeks 12 and 24 (r = −0.376 to −0.725, P = 0.031 to <0.001). Similarly, significant correlations at week 24 were also found for body fat percentage at baseline and the relative change in body fat percentage (r = −0.450, P = 0.006), for the absolute values of total fat at baseline and the corresponding relative change (r = −0.364, P = 0.037), and for total fat and abdominal fat mass at baseline and the relative change in body fat percentage (r = −0.458, P = 0.006; r = 0.431, P = 0.006, respectively). In addition, absolute values of 1RM strength at baseline were significantly correlated with relative changes in body fat percentage and relative changes of total and abdominal fat mass obtained at weeks 12 and 24 (r = −0.365 to −0.456, P = 0.025–0.006). Similarly, changes in 1RM strength performance and changes in leg lean mass and VL CSA were significantly correlated (r = 0.476–0.629, P = 0.037–0.007) at week 24.
Physical fitness, body composition, and blood lipid levels are strongly associated with health and mortality even in relatively young and healthy subjects (23,30). The purpose of the present study was to assess the effects of exercise order of moderate-frequency (2–3 times per week) endurance and strength training combined into the same training session (E+S vs S+E) on physical fitness, body composition, and blood lipid levels in moderately active and healthy young men. This study showed that both training orders (E+S and S+E) led to significant increases in muscular and cardiorespiratory fitness, muscle CSA, and lean body mass after 12 and 24 wk of training, but no reductions in total body or abdominal fat mass, body fat percentage, or blood lipid levels were observed in either of the two training groups. In addition, the magnitude of training-induced adaptations did not differ between the two groups.
Compared with concurrent training performed on separate days, endurance and strength training combined into the same training session does not allow any recovery between the two modes, leading to the second loading performed to be adversely affected by fatigue induced by the first loading. In recent studies, these adverse effects were reflected by increased work economy when endurance loading was performed immediately after a strength loading (13) and reduced neuromuscular performance measured immediately after intensive running or cycling (27), possibly influencing physiological training adaptations. As previous studies of combined endurance and strength training have shown possible compromised adaptations in strength and power but not endurance performance (21), it is likely that the acute effects of endurance loading on strength performance are more critical for the long-term development of physical fitness than the acute effects of strength loading on work economy during endurance performance.
Interestingly, the present E+S and S+E training groups significantly improved physical fitness, as reflected in 1RM strength (12%–17%), MVCmax (10%–13%), time to exhaustion (15%–17%), aerobic power (13%–16%), and V˙O2max (7%), to a similar extent and no between-group differences were observed. Our findings are in line with results of Collins and Snow (12) and Chtara et al. (9) who also reported that either loading order was similarly effective in improving endurance and strength performance after prolonged combined E+S or S+E training. However, other studies have found limited increases in V˙O2max after the E+S order in women (20) or S+E order in men (10) and impaired strength adaptations after E+S training in older men (8) when compared with the reverse loading order. Despite these findings of studies combining endurance and strength training into the same training session and those that report diverse biological adaptations induced by endurance and strength training alone (22), the present results indicate that our subjects adapted to both training stimuli simultaneously and to the similar magnitude.
When combining endurance and strength into the same training session, it seems that the type of endurance training performed needs to be carefully considered. Endurance cycling is biomechanically similar to many of the strength exercises performed in the present study (16) and may essentially lead to a similar magnitude of fatigue as indicated, for example, by inhibited neuromuscular performance observed during a single isometric contraction (32,33), suggesting similar acute neural responses to both types of loadings. Furthermore, previous studies have shown that endurance cycling training may also lead to small but significant increases in muscle CSA (28) and strength (24) in physically active subjects with no experience in regular endurance or strength training. Therefore, the present endurance cycling combined with the hypertrophic and maximal strength training protocols may have led to synergistic rather than adverse effects on strength and endurance performance. This hypothesis may also be supported by the review by Wilson et al. (40) who revealed that endurance running may be more detrimental to strength adaptations when compared with endurance cycling, possibly related to a larger magnitude of muscle damage induced by the eccentric components of prolonged running (29).
The present increases in 1RM strength were significantly correlated with increases in anatomical muscle CSA and leg lean mass in all subjects across the two training groups. Both training groups significantly increased muscle CSA after the 24 wk of training, independent of the loading order. Although animal studies have shown that endurance and strength training might induce distinct genetic and molecular pathways critical for muscle hypertrophy (4,22), other studies of human subjects have indicated the cumulative effect of both loadings to possibly compromise beneficial morphological adaptations (11,22). Coffey et al. (11) found in an acute study that neither of the two loading orders (E+S vs S+E) showed superior signaling responses over the other but concluded that endurance and strength training performed in close proximity did not induce optimal activation of pathways to promote significant anabolic processes. Although the magnitude of interference when compared with strength training alone was beyond the scope of this study, these previous findings possibly explain why no between-group differences in muscle growth were observed.
Similar to anatomical muscle CSA, leg, upper body, and total lean mass were increased in the present two groups during the 24 wk of training, independent of loading order. Muscle strength and possibly muscle mass have been associated with reduced mortality even in young subjects (30). Because lean body mass has been shown to be a major determinant of basal metabolic rate by representing 60%–75% of an individual’s daily energy expenditure (35), increases in muscle and lean mass may have potential health benefits by inducing enhanced fat oxidation (14,36). Our findings are thus of great importance because they show that a moderate volume of combined endurance and strength training may be beneficial in significantly increasing muscle strength and lean mass whereby the loading order does not seem to influence the magnitude of these adaptations.
However, the positive adaptations in physical fitness and lean body mass were not accompanied by significant reductions in body fat percentage and total or abdominal fat mass in either training group. Furthermore, no significant changes in total cholesterol, HDL-C and LDL-C, or triglyceride levels were observed. Previous studies have shown a strong association between body fat and blood lipid levels (6), indicating that a reduction in fat mass positively correlates to changes in blood lipid levels. Typically, aerobic exercise has been considered as being most effective to induce reductions in fat oxidation during and in the hours after an exercise loading (14,38), whereas the direct effects of strength training on reductions in body fat and blood lipids are minimal (19,26). Studies combining endurance and strength training on separate days often show reductions in both variables, with varying training frequency and volume in young (19) and old men (34) as well as in old women (15). Therefore, our results may indicate endurance and strength training combined into the same training session to be less favorable for reductions in body fat and blood lipid levels than combined training performed on separate days. In contrast to our study, however, it needs to be noted that most of the previous studies were performed with endurance running. Achten et al. (1) showed that running induces higher rates of fat oxidation when compared with those in cycling, and a meta-analysis by Wilson et al. (40) found combined training programs, in which the aerobic training is carried out by running, to be possibly more beneficial in reducing body fat when compared with endurance cycling, which may provide additional explanations for our findings compared with those of previous investigations.
In addition, the important difference of the present study design compared with combined studies in which endurance and strength training was performed on separate days is that by performing both types of loadings subsequently in the same training session, the total training frequency is essentially reduced (2–3× 1E+S or 2–3× 1S+E per week = 2–3 total sessions instead of 2–3× 1S + 2–3× 1E per week = 4–6 total sessions). Although energy expenditure (as measured by postexercise oxygen consumption) during exercise increases in proportion to the work performed, it does not return to baseline immediately postexercise but may remain elevated for a prolonged time (7). Previous studies have shown a dose–response relation between the duration and magnitude of postexercise oxygen consumption and the duration and intensity of both endurance and strength loadings performed (7), but very few studies have directly compared the effects of splitting exercise sessions with the similar workload performed during only one session. From these studies, however, it seems that performing prolonged endurance cycling (3) may lead to a smaller overall increase in postexercise oxygen consumption when compared with the same workload performed in two separate exercise sessions. Because we decreased the overall training frequency in the present study by combining endurance and strength training into the same training session, the overall weekly energy expenditure may have been lower than that observed during conventional concurrent training programs (i.e., separate-day combined training). However, because postexercise oxygen consumption or energy expenditure was not measured in this study, these speculations remain to be investigated.
Further possible explanations for our findings of no significant reductions in body fat and blood lipid levels may be related to the present endurance training program. In line with our purpose to provide a moderate-volume training program, we limited the duration of each training session to a maximum of 100 min, leading to a total of maximal 200 min during weeks 0–12 and 200–300 min during weeks 13–24. Because only half of the total training time was performed as endurance cycling, the overall duration and intensity of aerobic training may not have been sufficient (as also observed by the relatively small increases in V˙O2max) to result in significant reductions of body fat and changes in blood lipid levels.
Lastly, when interpreting the present results, one must bear in mind that the subjects of the present study were normal-weight, moderately active, and healthy males with normal blood lipid levels, which in turn provided a relatively small window for adaptations (14). Moreover, the nutritional intake was controlled but not restricted and the analysis of food diaries revealed that the subjects in both training groups maintained their caloric intake constant throughout the 24 wk of training, which may support the finding that no significant changes in fat mass and blood lipids were observed. However, the observed correlations between the present absolute values of fat mass and body fat percentage and the relative reductions in these variables observed after 24 wk of training in all subjects independent of the training group indicate that our training program was especially effective for subjects with an initially high percentage of body fat, suggesting that the present training program may be desirable for overweight or obese populations.
In conclusion, this study demonstrated that both endurance training immediately followed by strength training and the reversed loading order are beneficial in enhancing physical fitness and body composition in healthy, moderately active subjects even when the training frequency and volume are moderate. Although no significant reductions in body fat and blood lipids were observed, the significant increases in lean body mass may provide prolonged health benefits with the present training design. However, further studies should compare endurance and strength training combined into the same training session with that performed on separate days by possibly modifying the type and volume of endurance training performed, providing dietary restrictions, or including additional populations such as overweight, obese, or elderly subjects.
The authors express their gratitude to the technical staff involved in the data collection and would like to acknowledge the subjects who made this data collection possible.
The funding for this study has been provided by the Finnish Ministry of Education and Culture.
The authors do not have conflicts of interests.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:© 2014 American College of Sports Medicine
ORDER EFFECT; AEROBIC TRAINING; RESISTANCE TRAINING; CONCURRENT ENDURANCE AND STRENGTH TRAINING; MUSCLE CROSS-SECTIONAL AREA; BODY COMPOSITION; HYPERTROPHY; HEALTH