Lorena Rodríguez-García

Limitations to oxygen transport and utilization during sprint exercise in humans: evidence for a functional reserve in muscle O2 diffusing capacity

Severe acute hypoxia reduces sprint performance. Muscle V̇O2 during sprint exercise in normoxia is not limited by O2 delivery, O2 offloading from haemoglobin or structure‐dependent diffusion constraints in the skeletal muscle of young healthy men. A large functional reserve in muscle O2 diffusing capacity exists and remains available at exhaustion during exercise in normoxia; this functional reserve is recruited during exercise in hypoxia. During whole‐body incremental exercise to exhaustion in severe hypoxia, leg V̇O2 is primarily dependent on convective O2 delivery and less limited by diffusion constraints than previously thought. The kinetics of O2 offloading from haemoglobin does not limit V̇O2 peak in hypoxia. Our results indicate that the limitation to V̇O2 during short sprints resides in mechanisms regulating mitochondrial respiration.

Increased oxidative stress and anaerobic energy release, but blunted Thr172-AMPKα phosphorylation, in response to sprint exercise in severe acute hypoxia in humans

AMP-activated protein kinase (AMPK) is a major mediator of the exercise response and a molecular target to improve insulin sensitivity. To determine if the anaerobic component of the exercise response, which is exaggerated when sprint is performed in severe acute hypoxia, influences sprint exercise-elicited Thr(172)-AMPKα phosphorylation, 10 volunteers performed a single 30-s sprint (Wingate test) in normoxia and in severe acute hypoxia (inspired Po(2): 75 mmHg). Vastus lateralis muscle biopsies were obtained before and immediately after 30 and 120 min postsprint. Mean power output and O(2) consumption were 6% and 37%, respectively, lower in hypoxia than in normoxia. O(2) deficit and muscle lactate accumulation were greater in hypoxia than in normoxia. Carbonylated skeletal muscle and plasma proteins were increased after the sprint in hypoxia. Thr(172)-AMPKα phosphorylation was increased by 3.1-fold 30 min after the sprint in normoxia. This effect was prevented by hypoxia. The NAD(+)-to-NADH.H(+) ratio was reduced (by 24-fold) after the sprints, with a greater reduction in hypoxia than in normoxia (P < 0.05), concomitant with 53% lower sirtuin 1 (SIRT1) protein levels after the sprint in hypoxia (P < 0.05). This could have led to lower liver kinase B1 (LKB1) activation by SIRT1 and, hence, blunted Thr(172)-AMPKα phosphorylation. Ser(485)-AMPKα(1)/Ser(491)-AMPKα(2) phosphorylation, a known negative regulating mechanism of Thr(172)-AMPKα phosphorylation, was increased by 60% immediately after the sprint in hypoxia, coincident with increased Thr(308)-Akt phosphorylation. Collectively, our results indicate that the signaling response to sprint exercise in human skeletal muscle is altered in severe acute hypoxia, which abrogated Thr(172)-AMPKα phosphorylation, likely due to lower LKB1 activation by SIRT1.

Critical role for free radicals on sprint exercise-induced CaMKII and AMPKα phosphorylation in human skeletal muscle.

The extremely high energy demand elicited by sprint exercise is satisfied by an increase in O2 consumption combined with a high glycolytic rate, leading to a marked lactate accumulation, increased AMP-to-ATP ratio, and reduced NAD(+)/NADH.H(+) and muscle pH, which are accompanied by marked Thr(172) AMP-activated protein kinase (AMPK)-α phosphorylation during the recovery period by a mechanism not fully understood. To determine the role played by reactive nitrogen and oxygen species (RNOS) on Thr(172)-AMPKα phosphorylation in response to cycling sprint exercise, nine voluntary participants performed a single 30-s sprint (Wingate test) on two occasions: one 2 h after the ingestion of placebo and another after the intake of antioxidants (α-lipoic acid, vitamin C, and vitamin E) in a double-blind design. Vastus lateralis muscle biopsies were obtained before, immediately postsprint, and 30 and 120 min postsprint. Performance and muscle metabolism were similar during both sprints. The NAD(+)-to-NADH.H(+) ratio was similarly reduced (84%) and the AMP-to-ATP ratio was similarly increased (×21-fold) immediately after the sprints. Thr(286) Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and Thr(172)-AMPKα phosphorylations were increased after the control sprint (with placebo) but not when the sprints were preceded by the ingestion of antioxidants. Ser(485)-AMPKα1/Ser(491)-AMPKα2 phosphorylation, a known inhibitory mechanism of Thr(172)-AMPKα phosphorylation, was increased only with antioxidant ingestion. In conclusion, RNOS play a crucial role in AMPK-mediated signaling after sprint exercise in human skeletal muscle. Antioxidant ingestion 2 h before sprint exercise abrogates the Thr(172)-AMPKα phosphorylation response observed after the ingestion of placebo by reducing CaMKII and increasing Ser(485)-AMPKα1/Ser(491)-AMPKα2 phosphorylation. Sprint performance, muscle metabolism, and AMP-to-ATP and NAD(+)-to-NADH.H(+) ratios are not affected by the acute ingestion of antioxidants.

Androgen Receptor Gene Polymorphisms and the Fat‐Bone Axis in Young Men and Women

Androgen receptor (AR) CAG(n) (polyglutamine) and GGN(n) (polyglycine) repeat polymorphisms determine part of the androgenic effect and may influence adiposity. The association of fat mass, and its regional distribution, with the AR CAG(n) and GGN(n) polymorphisms was studied in 319 and 78 physically active nonsmoker men and women (mean ± SD: 28.3 ± 7.6 and 24.8 ± 6.2 years old, respectively). The length of CAG and GGN repeats was determined by polymerase chain reaction and fragment analysis, and confirmed by DNA sequencing of selected samples. Men were grouped as CAG short (CAG(S)) if harboring repeat lengths ≤ 21, the rest as CAG long (CAG(L)). The corresponding cutoff CAG number for women was 22. GGN was considered short (GGN(S)) if GGN ≤ 23, the rest as GGN long (GGN(L)). No association between AR polymorphisms and adiposity or the hormonal variables was observed in men. Neither was there a difference in the studied variables between men harboring CAG(L) + GGN(L),CAG(S) + GGN(S),CAG(S) + GGN(L), and CAG(L) + GGN(S) combinations. However, in women, GGN(n) was linearly related to the percentage of body fat (r = 0.30, P < .05), the percentage of fat in the trunk (r = 0.28, P < .05), serum leptin concentration (r = 0.40, P < .05), and serum osteocalcin concentration (r = 0.32, P < .05). In men, free testosterone was inversely associated with adiposity and serum leptin concentration, and positively with osteocalcin, even after accounting for differences in CAG(n), GGN(n), or both. In summary, this study shows that the AR repeat polymorphism has little influence on absolute and relative fat mass or its regional distribution in physically active men. In young women, GGN length is positively associated with adiposity, leptin, and osteocalcin.

Androgen receptor gene polymorphism influence fat accumulation: A longitudinal study from adolescence to adult age

To determine the influence of androgen receptor CAG and GGN repeat polymorphisms on fat mass and maximal fat oxidation (MFO), CAG and GGN repeat lengths were measured in 128 young boys, from which longitudinal data were obtained in 45 of them [mean ± SD: 12.8 ± 3.6 years old at recruitment, and 27.0 ± 4.8 years old at adult age]. Subjects were grouped as CAG short (CAGS) if harboring repeat lengths ≤  21, the rest as CAG long (CAGL); and GGN short (GGNS) if GGN repeat lengths ≤  23, or long if >  23 (GGNL). CAGS and GGNS were associated with lower adiposity than CAGL or GGNL (P < 0.05). There was an association between the logarithm of CAG repeats polymorphism and the changes of body mass (r = 0.34, P = 0.03). At adult age, CAGS men showed lower accumulation of total body and trunk fat mass, and lower resting metabolic rate (RMR) and MFO per kg of total lean mass compared with CAGL (P < 0.05). GGNS men also showed lower percentage of body fat (P < 0.05). In summary, androgen receptor CAG and GGN repeat polymorphisms are associated with RMR, MFO, fat mass, and its regional distribution in healthy male adolescents, influencing fat accumulation from adolescence to adult age.

Isoinertial and Isokinetic Sprints: Muscle Signalling

To determine if the muscle signalling response to a 30 s all-out sprint exercise is modulated by the exercise mode and the endocrine response, 27 healthy volunteers were divided in 2 groups that performed isokinetic (10 men and 5 women) and isoinertial (7 men and 5 women) Wingate tests. Blood samples and vastus lateralis muscle biopsies were taken before, immediately after, 30 and 120 min after the sprints. Groups were comparable in age, height, body weight, percentage of body fat, peak power per kg of lower extremities lean mass (Pmax) and muscle fibre types. However, the isoinertial group achieved a 25% greater mean power (Pmean). Sprint exercise elicited marked increases in the musculus vastus lateralis AMPKα, ACCβ, STAT3, STAT5 and ERK1/2 phosphorylation (all P<0.05). The AMPKα, STAT3, and ERK1/2 phosphorylation responses were more marked after the isoinertial than isokinetic test (interaction: P<0.01). The differences in muscle signalling could not be accounted for by differences in Pmax, although Pmean could explain part of the difference in AMPKα phosphorylation. The leptin, insulin, glucose, GH, IL-6, and lactate response were similar in both groups. In conclusion, the muscle signalling response to sprint exercise differs between isoinertial and isokinetic sprints.

Greater basal skeletal muscle AMPKα phosphorylation in men than in women: Associations with anaerobic performance

Abstract Objectives: This study was designed to investigate the association of gender, fibre type composition, and anaerobic performance with the basal skeletal muscle signalling cascades regulating muscle phenotype. Design: Muscle biopsies were obtained from 25 men and 10 women all young and healthy. Methods. Protein phosphorylation of Thr172AMPKα, Ser221ACCβ, Thr286CaMKII as well as total protein abundance of PGC-1α, SIRT1, and CnA were measured by Western blot and anaerobic performance by the Wingate test. Results: Percent type I myosin heavy chain (MHC I) was lower in men (37.1 ± 10.4 vs. 58.5 ± 12.5, P < .01). Total, free testosterone and free androgen index were higher in men (11.5, 36.6 and 40.6 fold, respectively, P < .01). AMPKα phosphorylation was 2.2-fold higher in men compared to women (P < .01). Total Ser221ACCβ and Thr286CaMKII fractional phosphorylation tended to be higher in men (P = .1). PGC1-α and SIRT1 total protein expression was similar in men and women, whereas CnA tended to be higher in men (P = .1). Basal AMPKα phosphorylation was linearly related to the percentage of MHC I in men (r = 0.56; P < .01), but not in women. No association was observed between anaerobic performance and basal phosphorylations in men and women, analysed separately. Conclusion: In summary, skeletal muscle basal AMPKα phosphorylation is higher in men compared to women, with no apparent effect on anaerobic performance.