Monique Ramaekers

Beneficial metabolic adaptations due to endurance exercise training in the fasted state

Training with limited carbohydrate availability can stimulate adaptations in muscle cells to facilitate energy production via fat oxidation. Here we investigated the effect of consistent training in the fasted state, vs. training in the fed state, on muscle metabolism and substrate selection during fasted exercise. Twenty young male volunteers participated in a 6-wk endurance training program (1-1.5 h cycling at ∼70% Vo(₂max), 4 days/wk) while receiving isocaloric carbohydrate-rich diets. Half of the subjects trained in the fasted state (F; n = 10), while the others ingested ample carbohydrates before (∼160 g) and during (1 g·kg body wt⁻¹·h⁻¹) the training sessions (CHO; n = 10). The training similarly increased Vo(₂max) (+9%) and performance in a 60-min simulated time trial (+8%) in both groups (P < 0.01). Metabolic measurements were made during a 2-h constant-load exercise bout in the fasted state at ∼65% pretraining Vo(₂max). In F, exercise-induced intramyocellular lipid (IMCL) breakdown was enhanced in type I fibers (P < 0.05) and tended to be increased in type IIa fibers (P = 0.07). Training did not affect IMCL breakdown in CHO. In addition, F (+21%) increased the exercise intensity corresponding to the maximal rate of fat oxidation more than did CHO (+6%) (P < 0.05). Furthermore, maximal citrate synthase (+47%) and β-hydroxyacyl coenzyme A dehydrogenase (+34%) activity was significantly upregulated in F (P < 0.05) but not in CHO. Also, only F prevented the development exercise-induced drop in blood glucose concentration (P < 0.05). In conclusion, F is more effective than CHO to increase muscular oxidative capacity and at the same time enhances exercise-induced net IMCL degradation. In addition, F but not CHO prevented drop of blood glucose concentration during fasting exercise.

Exercise in the fasted state facilitates fibre type-specific intramyocellular lipid breakdown and stimulates glycogen resynthesis in humans

The effects were compared of exercise in the fasted state and exercise with a high rate of carbohydrate intake on intramyocellular triglyceride (IMTG) and glycogen content of human muscle. Using a randomized crossover study design, nine young healthy volunteers participated in two experimental sessions with an interval of 3 weeks. In each session subjects performed 2 h of constant‐load bicycle exercise (∼75%), followed by 4 h of controlled recovery. On one occasion they exercised after an overnight fast (F), and on the other (CHO) they received carbohydrates before (∼150 g) and during (1 g (kg bw)−1 h−1) exercise. In both conditions, subjects ingested 5 g carbohydrates per kg body weight during recovery. Fibre type‐specific relative IMTG content was determined by Oil red O staining in needle biopsies from m. vastus lateralis before, immediately after and 4 h after exercise. During F but not during CHO, the exercise bout decreased IMTG content in type I fibres from 18 ± 2% to 6 ± 2% (P= 0.007) area lipid staining. Conversely, during recovery, IMTG in type I fibres decreased from 15 ± 2% to 10 ± 2% in CHO, but did not change in F. Neither exercise nor recovery changed IMTG in type IIa fibres in any experimental condition. Exercise‐induced net glycogen breakdown was similar in F and CHO. However, compared with CHO (11.0 ± 7.8 mmol kg−1 h−1), mean rate of postexercise muscle glycogen resynthesis was 3‐fold greater in F (32.9 ± 2.7 mmol kg−1 h−1, P= 0.01). Furthermore, oral glucose loading during recovery increased plasma insulin markedly more in F (+46.80 μU ml−1) than in CHO (+14.63 μU ml−1, P= 0.02). We conclude that IMTG breakdown during prolonged submaximal exercise in the fasted state takes place predominantly in type I fibres and that this breakdown is prevented in the CHO‐fed state. Furthermore, facilitated glucose‐induced insulin secretion may contribute to enhanced muscle glycogen resynthesis following exercise in the fasted state.

Protective role of {alpha}-actinin-3 in the response to an acute eccentric exercise bout

The ACTN3 gene encodes for the alpha-actinin-3 protein, which has an important structural function in the Z line of the sarcomere in fast muscle fibers. A premature stop codon (R577X) polymorphism in the ACTN3 gene causes a complete loss of the protein in XX homozygotes. This study investigates a possible role for the alpha-actinin-3 protein in protecting the fast fiber from eccentric damage and studies repair mechanisms after a single eccentric exercise bout. Nineteen healthy young men (10 XX, 9 RR) performed 4 series of 20 maximal eccentric knee extensions with both legs. Blood (creatine kinase; CK) and muscle biopsy samples were taken to study differential expression of several anabolic (MyoD1, myogenin, MRF4, Myf5, IGF-1), catabolic (myostatin, MAFbx, and MURF-1), and contraction-induced muscle damage marker genes [cysteine- and glycine-rich protein 3 (CSRP3), CARP, HSP70, and IL-6] as well as a calcineurin signaling pathway marker (RCAN1). Baseline mRNA content of CSRP3 and MyoD1 was 49 + or - 12 and 67 + or - 25% higher in the XX compared with the RR group (P = 0.01-0.045). However, satellite cell number was not different between XX and RR individuals. After eccentric exercise, XX individuals tended to have higher serum CK activity (P = 0.10) and had higher pain scores than RR individuals. However, CSRP3 (P = 0.058) and MyoD1 (P = 0.08) mRNA expression tended to be higher after training in RR individuals compared with XX alpha-actinin-3-deficient subjects. This study suggests a protective role of alpha-actinin-3 protein in muscle damage after eccentric training and an improved stress-sensor signaling, although effects are small.

Soleus muscles of SAMP8 mice provide an accelerated model of skeletal muscle senescence

Animal models are valuable research tools towards effective prevention of sarcopenia and towards a better understanding of the mechanisms underlying skeletal muscle aging. We investigated whether senescence-accelerated mouse (SAM) strains provide valid models for skeletal muscle aging studies. Male senescence-prone mice SAMP6 and SAMP8 were studied at age 10, 25 and 60 weeks and compared with senescence-resistant strain, SAMR1. Soleus and EDL muscles were tested for in vitro contractile properties, phosphocreatine content, muscle mass and fiber-type distribution. Declined muscle mass and contractility were observed at 60 weeks, the differences being more pronounced in SAMP8 than SAMP6 and more pronounced in soleus than EDL. Likewise, age-related decreases in muscle phosphocreatine content and type-II fiber size were most pronounced in SAMP8 soleus. In conclusion, typical features of muscular senescence occur at relatively young age in SAMP8 and nearly twice as fast as compared with other models. We suggest that soleus muscles of SAMP8 mice provide a cost-effective model for muscular aging studies.

No effect of dietary nitrate supplementation on endurance training in hypoxia

We investigated whether dietary nitrate (NO3−) supplementation enhances the effect of training in hypoxia on endurance performance at sea level. Twenty‐two healthy male volunteers performed high‐intensity endurance training on a cycle ergometer (6 weeks, 5×30 min/week at 4–6 mmol/L blood lactate) in normobaric hypoxia (12.5% FiO2), while ingesting either beetroot juice [0.07 mmol NO3−/kg body weight (bw)/day; BR, n = 11] or a control drink (CON, n = 11). During the pretest and the posttest, the subjects performed a 30‐min simulated time trial (TT) and an incremental VO2max test. Furthermore, a biopsy was taken from m. vastus lateralis before and after the TT. Power output during the training sessions in both groups increased by ∼6% from week 1 to week 6 (P < 0.05). Compared with the pretest, VO2max in the posttest was increased (P < 0.05) in CON (5%) and BR (9%). Power output corresponding with the 4 mmol/L blood lactate threshold, as well as mean power output during TT increased by ∼16% in both groups (P < 0.05). Muscle phospho‐AMP‐activated protein kinase, hypoxia inducible factor‐1α mRNA content, and glycogen breakdown during the TT were similar between the groups in both the pretest and the posttest. In conclusion, low‐dose dietary NO3− supplementation does not enhance the effects of intermittent hypoxic training on endurance exercise performance at sea level.

Effect of muscle creatine content manipulation on contractile properties in mouse muscles

The effects of muscle creatine manipulation on contractile properties in oxidative and glycolytic muscles were evaluated. Whereas control mice (NMRi; n = 12) received normal chow (5 g daily), three experimental groups were created by adding creatine monohydrate (CR group; 5%, 1 week; n = 13); β‐guanidinoproprionic acid, an inhibitor of cellular creatine uptake (β‐GPA group; 1%, 2 weeks; n = 12); or CR following β‐GPA (β‐GPA+CR group; n = 11). Total creatine (TCr) and the contractile properties of incubated soleus and extensor digitorum longus (EDL) muscles were determined. For the soleus, compared with control, TCr increased in the CR group (+25%), decreased in β‐GPA group (−50%), and remained stable in the β‐GPA+CR group, whereas, for the EDL, TCr was similar in the CR, and lower in the β‐GPA (−40%) and β‐GPA+CR (−15%) groups. None of the experimental groups (CR, β‐GPA, or β‐GPA+CR) showed changes in peak tension (Ppeak), time to peak tension, or relaxation in soleus or EDL during twitch or tetanic stimulation. For the soleus, fatigue reduced Ppeak to ∼60% of initial Ppeak; 5 min of recovery restored Ppeak to values ∼15% higher in CR than in controls. Ppeak recovery was not affected by β‐GPA or β‐GPA+CR in the soleus or any treatment in the EDL. Thus, peak tension recovery is enhanced by creatine intake in oxidative but not glycolytic muscles. This may be implicated in the beneficial action of creatine loading. Muscle Nerve 29: 428–435, 2004

Alpha‐actinin‐3 deficiency does not significantly alter oxidative enzyme activity in fast human muscle fibres

Aim:  In Western European populations, about 18% of all individuals have a complete deficiency of the alpha‐actinin‐3 protein owing to homozygosity for a stop codon mutation (R577X) in the ACTN3 gene. Actn3−/− knock‐out mice show increased activity of multiple enzymes in the aerobic metabolic pathway in fast muscle fibres. Whether this observation is also present in human XX genotype carriers compared to RR carriers has not been studied in a fibre‐type‐specific approach in humans. The purpose of this study was therefore to compare fibre‐type‐specific oxidative enzyme activity in humans with a different ACTN3 R577X genotype.

Additive insulinogenic action of Opuntia ficus-indica cladode and fruit skin extract and leucine after exercise in healthy males.

BackgroundOral intake of a specific extract of Opuntia ficus-indica cladode and fruit skin (OpunDia™) (OFI) has been shown to increase serum insulin concentration while reducing blood glucose level for a given amount of glucose ingestion after an endurance exercise bout in healthy young volunteers. However, it is unknown whether OFI-induced insulin stimulation after exercise is of the same magnitude than the stimulation by other insulinogenic agents like leucine as well as whether OFI can interact with those agents. Therefore, the aims of the present study were: 1) to compare the degree of insulin stimulation by OFI with the effect of leucine administration; 2) to determine whether OFI and leucine have an additive action on insulin stimulation post-exercise.MethodsEleven subjects participated in a randomized double-blind cross-over study involving four experimental sessions. In each session the subjects successively underwent a 2-h oral glucose tolerance test (OGTT) after a 30-min cycling bout at ~70% VO2max. At t0 and t60 during the OGTT, subjects ingested 75 g glucose and capsules containing either 1) a placebo; 2) 1000 mg OFI; 3) 3 g leucine; 4) 1000 mg OFI + 3 g leucine. Blood samples were collected before and at 30-min intervals during the OGTT for determination of blood glucose and serum insulin.ResultsWhereas no effect of leucine was measured, OFI reduced blood glucose at t90 by ~7% and the area under the glucose curve by ~15% and increased serum insulin concentration at t90 by ~35% compared to placebo (P<0.05). From t60 to the end of the OGTT, serum insulin concentration was higher in OFI+leucine than in placebo which resulted in a higher area under the insulin curve (+40%, P<0.05).ConclusionCarbohydrate-induced insulin stimulation post-exercise can be further increased by the combination of OFI with leucine. OFI and leucine could be interesting ingredients to include together in recovery drinks to resynthesize muscle glycogen faster post-exercise. Still, it needs to be confirmed that such nutritional strategy effectively stimulates post-exercise muscle glycogen resynthesis.

High-fat diet overrules the effects of training on fiber-specific intramyocellular lipid utilization during exercise

In this study, we compared the effects of endurance training in the fasted state (F) vs. the fed state [ample carbohydrate intake (CHO)] on exercise-induced intramyocellular lipid (IMCL) and glycogen utilization during a 6-wk period of a hypercaloric (∼+30% kcal/day) fat-rich diet (HFD; 50% of kcal). Healthy male volunteers (18-25 yrs) received a HFD in conjunction with endurance training (four times, 60-90 min/wk) either in F (n = 10) or with CHO before and during exercise sessions (n = 10). The control group (n = 7) received a HFD without training and increased body weight by ∼3 kg (P < 0.001). Before and after a HFD, the subjects performed a 2-h constant-load bicycle exercise test in F at ∼70% maximal oxygen uptake rate. A HFD, both in the absence (F) or presence (CHO) of training, elevated basal IMCL content by ∼50% in type I and by ∼75% in type IIa fibers (P < 0.05). Independent of training in F or CHO, a HFD, as such, stimulated exercise-induced net IMCL breakdown by approximately twofold in type I and by approximately fourfold in type IIa fibers. Furthermore, exercise-induced net muscle glycogen breakdown was not significantly affected by a HFD. It is concluded that a HFD stimulates net IMCL degradation by increasing basal IMCL content during exercise in type I and especially IIa fibers. Furthermore, a hypercaloric HFD provides adequate amounts of carbohydrates to maintain high muscle glycogen content during training and does not impair exercise-induced muscle glycogen breakdown.

Intake of a Ketone Ester Drink during Recovery from Exercise Promotes mTORC1 Signaling but Not Glycogen Resynthesis in Human Muscle

Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown. Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL). Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C2C12 cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells. Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.