Intense resistance training induces pronounced metabolic stress and impairs hypertrophic response in hind-limb muscles of rats

Figures & data

Figure 1. Time-line diagram of jump-training protocol and subsequent blood sampling for analyses.

Table 1. Jump-training protocol.

Weeks	Sets × repetitions	Interval (seconds)	Load (% of body weight)
1	4 × 10	30	50
3	4 × 10	30	60
5	4 × 10	30	70

Jump-training performed by trained rats in weeks 1, 3, and 5. The protocol consisted of four sets of 10 repetitions with 30 s intervals. The load of training corresponded to 50, 60, and 70% of body weight in week 1, 3, and 5, respectively. n = 8.

Figure 2. Circulating lactate concentration measured at rest, immediately after, 20, 40, and 60 min post-training of trained rats (a). Plasma corticosterone concentrations (b) and creatine kinase activity (c) in non-trained and trained rats after 1, 3, or 5 weeks. Values are expressed as mean ± SEM. One-way ANOVA followed by Tukey’s post-test (p < .05): ^avs. previous time of lactate measurement; ^bvs. week 5; ^&vs. week 5 of non-trained group. n = 8/group.

Table 2. Body weight, absolute (MW) and relative (MW/BW) weights of soleus and extensor digitorum longus (EDL) muscles of non-trained and trained rats after 1, 3, or 5 weeks.

	Non-trained			Trained
Weeks	1	3	5	1	3	5
Body weight, g	298 ± 3	370 ± 9^a	401 ± 16^a,b	271 ± 5	297 ± 7^d	365 ± 13^a,b
Body weight gain (%)	–	24.5	34.6	–	9.6	34.7
Soleus
MW, mg	118 ± 1	152 ± 7^a	150 ± 4^a	109 ± 3	119 ± 3^d	138 ± 5^a
MW/BW, mg/g	0.395 ± 0	0.411 ± 0	0.375 ± 0	0.403 ± 0	0.397 ± 0	0.375 ± 0
EDL
MW, mg	133 ± 2	171 ± 4^a	168 ± 7^a	133 ± 3	143 ± 3^d	149^a,e ± 1
MW/BW, mg/g	0.446 ± 0	0.446 ± 0.1	0.449 ± 0	0.493 ± 0^c	0.479 ± 0^d	0.410 ± 0^a,b,e

MW: muscle weight; MW/BW: muscle weight-to-body weight ratio.

Values are expressed as mean ± SEM. Tukey’s post-test (p < .05): ^avs. week 1 of the same group; ^bvs. week 3 of the same group; ^cvs. week 1 of non-trained group; ^dvs. week 3 of non-trained group; ^evs. week 5 of non-trained group. n = 8/group.

Figure 3. Images of soleus (SOL) and extensor digitorum longus (EDL) muscles stained with hematoxylin and eosin (H&E) after 1, 3, or 5 weeks of the experimental period. Representative images were taken at 40x magnification. Groups: non-trained and trained rats. *vs. week 1 of the same group; ^#vs. week 3 of non-trained group; ^&vs. week 5 of non-trained group. n = 8/group.

Table 3. Cross-sectional area (CSA) of soleus and extensor digitorum longus (EDL) muscles of non-trained and trained rats after 1, 3, or 5 weeks.

	Non-trained			Trained
Weeks	1	3	5	1	3	5
Soleus, μm^2	2205 ± 109	3031 ± 132^a	2985 ± 128^a	2290 ± 104	2243 ± 96^b	2385 ± 104^c
EDL, μm^2	1627 ± 37	2058 ± 61^a	2105 ± 92^a	1946 ± 76	1909 ± 30	1725 ± 84^c

Values are expressed as mean ± SEM. Tukey’s post-test (p < .05): ^avs. week 1 of the same group; ^bvs. week 3 of non-trained group; ^cvs. week 5 of non-trained group. n = 8/group. CSA of ∼100 fibers from each animal was analyzed in four different regions (n = 8/group and ∼3200 fibers per group).

Figure 4. Relative myosin heavy chain (MHC) isoform distribution of MHC-I (a) and MHC-IIA (b) in soleus (SOL) muscle of non-trained and trained rats after 1, 3, or 5 weeks. Values are expressed as means ± SEM. One-way ANOVA followed by Tukey’s post-test (p < .05): ^&vs. week 5 of non-trained group. n = 8/group.

Figure 5. Relative myosin heavy chain (MHC) isoform expression of MHC-I (a), MHC-IIA (b), MHC-IID (c) and MHC-IIB (d) in extensor digitorum longus (EDL) muscle of non-trained and trained rats after 1, 3, or 5 weeks. Values are expressed as means ± SEM. No statistically significant differences: Kruskal–Wallis (p > .05). n = 8/group.