Antioxidants, Vol. 12, Pages 53: High-Intensity Exercise Training Alters the Effect of N-Acetylcysteine on Exercise-Related Muscle Ionic Shifts in Men

Figure 1. Schematic overview of the experimental protocol. Exp. day, experimental day; DXA, dual-energy X-ray absorptiometry; NAC, N-acetylcysteine; SET, speed endurance training group; SETSaline, right leg in SET (i.e., leg receiving saline infusion before and after the SET intervention); SETNAC, left leg in SET (i.e., leg receiving NAC infusion before and after the SET intervention); CON, control group; CONSaline, right leg in CON; CONNAC, left leg in CON.

Figure 1. Schematic overview of the experimental protocol. Exp. day, experimental day; DXA, dual-energy X-ray absorptiometry; NAC, N-acetylcysteine; SET, speed endurance training group; SETSaline, right leg in SET (i.e., leg receiving saline infusion before and after the SET intervention); SETNAC, left leg in SET (i.e., leg receiving NAC infusion before and after the SET intervention); CON, control group; CONSaline, right leg in CON; CONNAC, left leg in CON.

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Figure 2. Leg exercise performance without and with N-acetylcysteine infusion before and after speed endurance training (SET). Time to exhaustion during knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion before (Pre) and after (Post) SET as well as before and after habitual lifestyle maintenance (CON) for the right (CONSaline, n = 10) and left (CONNAC, n = 10) leg. ** Post different from Pre (p < 0.01). Data are presented as mean ± SD with individual changes.

Figure 2. Leg exercise performance without and with N-acetylcysteine infusion before and after speed endurance training (SET). Time to exhaustion during knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion before (Pre) and after (Post) SET as well as before and after habitual lifestyle maintenance (CON) for the right (CONSaline, n = 10) and left (CONNAC, n = 10) leg. ** Post different from Pre (p < 0.01). Data are presented as mean ± SD with individual changes.

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Figure 3. Effect of speed endurance training (SET) on femoral arterial plasma flow without and with N-acetylcysteine infusion. Femoral arterial plasma flow before, during, and after knee-extensor exercise without ((A), SETSaline, n = 10), and with N-acetylcysteine ((B), SETNAC, n = 9) infusion as well as difference (Δ) between SETNAC and SETSaline ((C), n = 9) before (Pre) and after (Post) SET. ** Post different from Pre (p < 0.05). * Post different from Pre (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 3. Effect of speed endurance training (SET) on femoral arterial plasma flow without and with N-acetylcysteine infusion. Femoral arterial plasma flow before, during, and after knee-extensor exercise without ((A), SETSaline, n = 10), and with N-acetylcysteine ((B), SETNAC, n = 9) infusion as well as difference (Δ) between SETNAC and SETSaline ((C), n = 9) before (Pre) and after (Post) SET. ** Post different from Pre (p < 0.05). * Post different from Pre (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 4. Effect of speed endurance training (SET) on plasma lactate− shifts without and with N-acetylcysteine infusion. Plasma lactate− concentrations (AC,EG) and net leg lactate− exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as difference (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). ## Trial × time effect (p < 0.01). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 4. Effect of speed endurance training (SET) on plasma lactate− shifts without and with N-acetylcysteine infusion. Plasma lactate− concentrations (AC,EG) and net leg lactate− exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as difference (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). ## Trial × time effect (p < 0.01). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 5. Effect of speed endurance training (SET) on plasma pH and H+ shifts without and with N-acetylcysteine infusion. Plasma pH (AC,EG) and net leg H+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). §§ Trial × leg effect (p < 0.01). § Trial × leg effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 5. Effect of speed endurance training (SET) on plasma pH and H+ shifts without and with N-acetylcysteine infusion. Plasma pH (AC,EG) and net leg H+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). §§ Trial × leg effect (p < 0.01). § Trial × leg effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 6. Effect of speed endurance training (SET) on plasma HCO3− shifts without and with N-acetylcysteine infusion. Plasma HCO3− concentrations (AF) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (GI, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). §§ Trial × leg effect (p < 0.01). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 6. Effect of speed endurance training (SET) on plasma HCO3− shifts without and with N-acetylcysteine infusion. Plasma HCO3− concentrations (AF) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (GI, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). §§ Trial × leg effect (p < 0.01). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 7. Effect of speed endurance training (SET) on plasma K+ shifts without and with N-acetylcysteine infusion. Plasma K+ concentrations (AC,EG) and net leg K+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). # Trial × time effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 7. Effect of speed endurance training (SET) on plasma K+ shifts without and with N-acetylcysteine infusion. Plasma K+ concentrations (AC,EG) and net leg K+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). # Trial × time effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 8. Effect of speed endurance training (SET) on plasma Na+ shifts without and with N-acetylcysteine infusion. Plasma Na+ concentrations (AC,EG) and net leg Na+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). # Trial × time effect (p < 0.05). § Trial × leg effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

Figure 8. Effect of speed endurance training (SET) on plasma Na+ shifts without and with N-acetylcysteine infusion. Plasma Na+ concentrations (AC,EG) and net leg Na+ exchange (D,H) before, during, and after knee-extensor exercise without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, n = 9) infusion as well as differences (Δ) between SETNAC and SETSaline (IL, n = 9) before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). # Trial × time effect (p < 0.05). § Trial × leg effect (p < 0.05). Data are presented as mean ± SEM (SETSaline and SETNAC) or mean ± 95% CI (Δ SETNAC − SETSaline).

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Figure 9. Effect of speed endurance training (SET) on muscle lactate− and pH at exhaustion without and with N-acetylcysteine infusion. Muscle [lactate−] ((A), SETSaline, n = 9; SETNAC, n = 8), muscle pH ((B), SETSaline, n = 8; SETNAC, n = 8), muscle [lactate−] gradient ((C), SETSaline, n = 9; SETNAC, n = 8), muscle [H+] gradient ((D), SETSaline, n = 8; SETNAC, n = 8) and the relationship between muscle gradients and net release ((E,F), SETSaline, n = 9; SETNAC, n = 8) immediately after knee-extensor exercise to exhaustion without (SETSaline) and with N-acetylcysteine (SETNAC) infusion before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). Data are presented as mean ± SD with individual changes (AD) or as mean ± SD (E,F).

Figure 9. Effect of speed endurance training (SET) on muscle lactate− and pH at exhaustion without and with N-acetylcysteine infusion. Muscle [lactate−] ((A), SETSaline, n = 9; SETNAC, n = 8), muscle pH ((B), SETSaline, n = 8; SETNAC, n = 8), muscle [lactate−] gradient ((C), SETSaline, n = 9; SETNAC, n = 8), muscle [H+] gradient ((D), SETSaline, n = 8; SETNAC, n = 8) and the relationship between muscle gradients and net release ((E,F), SETSaline, n = 9; SETNAC, n = 8) immediately after knee-extensor exercise to exhaustion without (SETSaline) and with N-acetylcysteine (SETNAC) infusion before (pre) and after (post) SET. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). Data are presented as mean ± SD with individual changes (AD) or as mean ± SD (E,F).

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Figure 10. Effect of speed endurance training (SET) on the muscle content of ion-handling proteins and antioxidant enzymes. Change in the muscle content of ion-handling proteins (AH) and antioxidant enzymes (IL) as well as representative blots (M) before (pre) to after (post) the SET intervention (SET, n = 10) or habitual lifestyle maintenance (CON, n = 9). NKA, Na+/K+-ATPase; FXYD1, regulatory subunit of NKA; Kir6.2, ATP-sensitive K+-channel subunit Kir6.2; MCT, monocarboxylate transporter; NHE1, Na+/H+ exchanger; SOD, superoxide dismutase; GPX, glutathione peroxidase. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.01). Data are presented as individual pre and post values and as mean fold change ± 95% CI relative to pre with individual changes.

Figure 10. Effect of speed endurance training (SET) on the muscle content of ion-handling proteins and antioxidant enzymes. Change in the muscle content of ion-handling proteins (AH) and antioxidant enzymes (IL) as well as representative blots (M) before (pre) to after (post) the SET intervention (SET, n = 10) or habitual lifestyle maintenance (CON, n = 9). NKA, Na+/K+-ATPase; FXYD1, regulatory subunit of NKA; Kir6.2, ATP-sensitive K+-channel subunit Kir6.2; MCT, monocarboxylate transporter; NHE1, Na+/H+ exchanger; SOD, superoxide dismutase; GPX, glutathione peroxidase. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.01). Data are presented as individual pre and post values and as mean fold change ± 95% CI relative to pre with individual changes.

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Figure 11. Effect of speed endurance training (SET) on the muscle content of ion-handling proteins and antioxidant enzymes. Phosphorylated FXYD1 (A) and representative blots (B) at rest and after knee-extensor exercise to exhaustion (exh.) without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, pre n = 9, post n = 10) infusion before (pre) and after (post) SET. * Exh. different from rest (p < 0.05). Data are presented as mean with individual changes.

Figure 11. Effect of speed endurance training (SET) on the muscle content of ion-handling proteins and antioxidant enzymes. Phosphorylated FXYD1 (A) and representative blots (B) at rest and after knee-extensor exercise to exhaustion (exh.) without (SETSaline, n = 10) and with N-acetylcysteine (SETNAC, pre n = 9, post n = 10) infusion before (pre) and after (post) SET. * Exh. different from rest (p < 0.05). Data are presented as mean with individual changes.

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Figure 12. Effect of speed endurance training (SET) on mitochondrial respiratory capacity. Mitochondrial respiratory capacity at different states before (pre) and after (post) SET ((A), SET, n = 10) or habitual lifestyle maintenance ((B), CON, n = 10). L, leak respiration; FAO, fatty acid oxidation; CID, complex I-linked respiration at sub-saturating ADP concentration; PD, complex I+II linked respiration at sub-saturating ADP concentration; P, maximal complex I+II linked respiration; E, maximal electron transfer-pathway capacity; ECII, complex II-linked electron transfer-pathway capacity. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). Data are presented as mean with individual changes.

Figure 12. Effect of speed endurance training (SET) on mitochondrial respiratory capacity. Mitochondrial respiratory capacity at different states before (pre) and after (post) SET ((A), SET, n = 10) or habitual lifestyle maintenance ((B), CON, n = 10). L, leak respiration; FAO, fatty acid oxidation; CID, complex I-linked respiration at sub-saturating ADP concentration; PD, complex I+II linked respiration at sub-saturating ADP concentration; P, maximal complex I+II linked respiration; E, maximal electron transfer-pathway capacity; ECII, complex II-linked electron transfer-pathway capacity. ** Post different from pre (p < 0.01). * Post different from pre (p < 0.05). Data are presented as mean with individual changes.

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Table 1. Subject characteristics at inclusion.

Table 1. Subject characteristics at inclusion.

SET (n = 10)CON (n = 10)Age (yr)23.0 ± 3.425.7 ± 3.7Height (cm)186 ± 6184 ± 6Body mass (kg)79.6 ± 12.176.0 ± 8.1BMI (kg·m−2)23.0 ± 2.522.4 ± 1.6V̇O2max (mL·min−1·kg−1)50.2 ± 4.552.8 ± 6.4

Table 2. Whole-body and thigh composition before and after speed endurance training (SET) or habitual lifestyle maintenance (CON).

Table 2. Whole-body and thigh composition before and after speed endurance training (SET) or habitual lifestyle maintenance (CON).

Whole-Body SETCONBody mass (kg)Pre79.6 ± 12.176.0 ± 8.1Post79.5 ± 11.675.9 ± 8.1Body fat mass (kg) #Pre16.2 ± 5.311.6 ± 3.4Post15.6 ± 4.911.5 ± 3.6Body fat percent (%)Pre20.0 ± 4.815.4 ± 5.2Post19.4 ± 4.7 *15.2 ± 5.2Body lean mass (kg)Pre60.4 ± 9.061.6 ± 8.6Post60.9 ± 8.961.5 ± 8.4Thigh SETSalineSETNACCONSalineCONNACThigh mass (g)Pre8817 ± 16218929 ± 14788532 ± 12208299 ± 1104Post8955 ± 15499085 ± 1380 *8497 ± 12448256 ± 1056Thigh fat mass (g)Pre1609 ± 5431650 ± 5361209 ± 3801190 ± 372Post1566 ± 5261606 ± 5241198 ± 4191194 ± 409Thigh fat percent (%)Pre18.1 ± 4.218.4 ± 4.614.3 ± 4.814.6 ± 5.1Post17.3 ± 4.3 *17.6 ± 4.614.2 ± 4.914.6 ± 5.1Thigh lean mass (g)Pre6943 ± 12637013 ± 11967054 ± 11586846 ± 1104Post7125 ± 1242 **7214 ± 1136 **7032 ± 11386799 ± 1019

Table 3. Effect of speed endurance training (SET) on cumulated net leg lactate−, H+, K+, and Na+ exchange during submaximal and intense exercise.

Table 3. Effect of speed endurance training (SET) on cumulated net leg lactate−, H+, K+, and Na+ exchange during submaximal and intense exercise.

Lactate−H+K+Na+ SETSalineSETNACSETSalineSETNACSETSalineSETNACSETSalineSETNACSubmaximal exercise (mmol)Pre21.9 ± 8.323.0 ± 9.850.3 ± 15.657.1 ± 12.13.2 ± 2.24.9 ± 2.312.5 ± 53.741.6 ± 43.0Post15.1 ± 5.7 **14.9 ± 8.2**42.4 ± 16.9 *47.8 ± 10.2 *2.1 ± 2.32.5 ± 3.3−5.8 ± 45.7−2.6 ± 119.0Submaximal exercise (mmol·min−1)Pre1.6 ± 0.61.7 ± 0.73.7 ± 1.04.1 ± 0.90.2 ± 0.20.3 ± 0.21.0 ± 4.13.0 ± 3.1Post1.1 ± 0.4 **1.1 ± 0.6 **3.1 ± 1.2 *3.4 ± 0.7 *0.2 ± 0.20.2 ± 0.2−0.4 ± 3.3−0.1 ± 8.6Incremental exercise to exh. (mmol)Pre4.2 ± 2.85.4 ± 4.66.7 ± 4.67.9 ± 5.50.6 ± 0.40.9 ± 0.7−6.3 ± 38.3−2.1 ± 8.4Post11.8 ± 5.6 **14.0 ± 6.1 **14.2 ± 5.0 **19.4 ± 7.0 **1.1 ± 1.71.2 ± 2.6−17.0 ± 62.7−21.4 ± 99.3Incremental exercise to exh. (mmol·min−1)Pre2.2 ± 1.32.6 ± 1.43.4 ± 1.93.6 ± 1.60.4 ± 0.30.4 ± 0.30.6 ± 15.1−1.2 ± 5.2Post3.0 ± 1.63.3 ± 1.63.6 ± 1.14.5 ± 1.40.3 ± 0.40.2 ± 0.7−4.1 ± 14.3−7.8 ± 29.3

Table 4. Correlation for change percentages in SETsaline for main outcomes.

Table 4. Correlation for change percentages in SETsaline for main outcomes.

Pearson’s Correlation Coefficient (r)p-ValueTime to exhaustionMuscle pH−0.520.189Muscle lactate0.000.994Leg lean mass−0.610.062NKA-α10.480.161NKA-α20.530.139NKA-β1−0.310.379FXYD10.040.914Venous plasma K+ during submaximal exercise
(measured at 80% Wmax)Leg lean mass−0.570.088NKA-α10.230.520NKA-α20.270.483NKA-β10.150.679FXYD10.010.985Mean net leg K+ release during submaximal exercise
(measured at 80% Wmax)Leg lean mass−0.560.092NKA-α10.170.640NKA-α20.320.399NKA-β1−0.440.199FXYD10.170.632Peak net leg K+ release
at exhaustionLeg lean mass0.200.579

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