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Unsweetened natural cocoa (UNCP) was evaluated for reproductive toxicity in rats. A preliminary genotoxic potential was evaluated by the DNA comet assay test using C57Bl/6 mice. Both therapeutic dose (TD; 900 mg/kg) and high dose (HD; 9000 mg/kg) of UNCP were used. White Wistar rats were used in two experimental groups. The females received UNCP 15 days before crossing with untreated males. The males received UNCP for 48 days before mating with untreated females. Subacute toxicity was observed during a 14-day oral administration of UNCP. Results show that a high tail DNA% was observed with methyl mesylate administration in all tissues analysed. The lowest tail DNA% value was observed in the liver (1.64 ± 0.26) and kidney (1.63 ± 0.30) during UNCP (TD) administration. UNCP did not induce observable physical congenital malformations on the pubs of treated female and male rats, lacks genotoxic potential, and did not adversely affect pregnancy index, pub weights, and survival index, but UNCP exhibited proimplantation potential (p>0.05).

As energetic metabolism is crucial for muscles, they develop different adaptations to respond to fluctuating demand among muscle types. Whereas quantitative characteristics are known, no study described simultaneously quantitative and qualitative differences among muscle types in terms of substrates utilization patterns. This study thus defined the pattern of substrates preferential utilization by mitochondria from glycolytic gastrocnemius (GAS) and oxidative soleus (SOL) skeletal muscles and from heart left ventrical (LV) in rats. We measured in situ, ADP (2 mM)-stimulated, mitochondrial respiration rates from skinned fibers in presence of increasing concentrations of pyruvate (Pyr)?+?malate (Mal), palmitoyl-carnitine (Palm-C)?+?Mal, glutamate (Glut)?+?Mal, glycerol-3-phosphate (G3-P), lactate (Lact)?+?Mal. Because the fibers oxygen uptake (Vs) followed MichaelisMenten kinetics in function of substrates level we determined the Vs and Km, representing maximal oxidative capacity and the mitochondrial sensibility for each substrate, respectively. Vs were in the order GAS?

Background: Attractive targeted sugar bait (ATSB) is a novel approach to vector control, offering an alternative mode of insecticide delivery via the insect alimentary canal, with potential to deliver a variety of compounds new to medical entomology and malaria control. Its potential to control mosquitoes was recently demonstrated in major field trials in Africa. The pyrrole chlorfenapyr is an insecticide new to malaria vector control, and through its unique mode of action-disruption of ATP mediated energy transfer in mitochondria-it may have direct action on energy transfer in the flight muscle cells of mosquitoes. It may also have potential to disrupt mitochondrial function in malarial parasites co-existing within the infected mosquito. However, little is known about the impact of such compounds on vector competence in mosquitoes responsible for malaria transmission., Methods: In this study, ATSBs containing chlorfenapyr insecticide and, as a positive control, the anti-malarial drugs artemether/lumefantrine (A/L) were compared for their effect on Plasmodium falciparum development in wild pyrethroid-resistant Anopheles gambiae sensu stricto (s.s.) and for their capacity to reduce vector competence. Female mosquitoes were exposed to ATSB containing either sublethal dose of chlorfenapyr (CFP: 0.025%) or concentrations of A/L ranging from 0.4/2.4 mg/ml to 2.4/14.4 mg/ml, either shortly before or after taking infective blood meals. The impact of their component compounds on the prevalence and intensity of P. falciparum infection were compared between treatments., Results: Both the prevalence and intensity of infection were significantly reduced in mosquitoes exposed to either A/L or chlorfenapyr, compared to unexposed negative control mosquitoes. The A/L dose (2.4/14.4 mg/ml) totally erased P. falciparum parasites: 0% prevalence of infection in female mosquitoes exposed compared to 62% of infection in negative controls (df = 1, χ 2  = 31.23 p < 0.001). The dose of chlorfenapyr (0.025%) that killed < 20% females in ATSB showed a reduction in oocyte density of 95% per midgut (0.18/3.43 per midgut)., Conclusion: These results are evidence that chlorfenapyr, in addition to its direct killing effect on the vector, has the capacity to block Plasmodium transmission by interfering with oocyte development inside pyrethroid-resistant mosquitoes, and through this dual action may potentiate its impact under field conditions., (© 2023. The Author(s).)

Objectives: To generate evidence on willingness to use HIV self-test kits and willingness to pay among antenatal care clients in public and private facilities in Cote d'Ivoire and Tanzania., Methods: Cross-sectional survey data were collected from 414 clients recruited from 35 high-volume facilities in Cote d'Ivoire and from 385 clients in 33 high-volume facilities in Tanzania. Surveys covered willingness to use HIV self-test kits, prices clients were willing to pay, advantages and disadvantages and views on specific qualities of HIV self-tests. Market data on availability of proxy self-testing products (e.g. pregnancy and malaria tests) and attitudes of pharmacists towards HIV self-test kits were collected from 51 pharmacies in Cote d'Ivoire and 59 in Tanzania., Results: Willingness to use HIV self-test kits was 65% in Cote d'Ivoire and 69% in Tanzania. Median ideal prices women would pay ranged from USD 1.77 in Cote d'Ivoire to USD 0.87 in Tanzania. Proxy self-test kits were available in pharmacies, and interest was high in stocking HIV self-test kits., Conclusions: Implications for national HIV self-test policy and planning include keeping prices low, providing psychological and HIV counselling, and ensuring linkage to HIV care and treatment services. Private pharmacies will play a key role in providing access to HIV self-test kits., (© 2020 The Authors Tropical Medicine & International Health Published by John Wiley & Sons Ltd.)

Impaired skeletal muscle energetic participates in peripheral arterial disease (PAD) patient's morbidity and mortality. Angiotensin converting enzyme inhibition (ACEi), cornerstone for pharmacologic risk factor management in PAD patients, might also be interesting by protecting skeletal muscle energetic. We therefore determined whether chronic ACEi might reduce ischemia-induced mitochondrial respiratory chain dysfunction in the frequent setting of hindlimb ischemia-reperfusion. Ischemic legs of rats submitted to 5 h ischemia induced by a rubber band tourniquet applied on the root of the hindlimb followed by reperfusion without (IR, n = 11) or after ACEi (n = 14; captopril 40 mg/kg per day during 28 days before surgery) were studied and compared to that of sham-operated animals (n = 11). The effect of ACEi on the non-ischemic contralateral leg was also determined in the ACEi group. Maximal oxidative capacities (V(max)) and complexes I, II and IV activities of the mitochondrial respiratory chain of the gastrocnemius muscle were determined using glutamate-malate, succinate and TMPD-ascorbate substrates. Arterial blood pressure was significantly decreased after ACEi (124 +/- 2.8 vs. 108 +/- 4.19 mmHg; P = 0.01). Ischemia-reperfusion reduced V(max) (4.4 +/- 0.4 vs. 8.7 +/- 0.5 micromol O2/min/g dry weight, -49%, P < 0.001), affecting mitochondrial complexes I, II and IV activities. ACEi failed to modulate ischemia-induced dysfunction (V(max) 5.1 +/- 0.7 micromol O2/min/g dry weight) or the non-ischemic contralateral muscle respiratory rate. Ischemia-reperfusion significantly impaired the mitochondrial respiratory chain I, II and IV complexes of skeletal muscle. Pharmacologic pre-treatment with ACEi did not prevent or increase such alterations. Further studies might be useful to improve the pharmacologic conditioning of PAD patients needing arterial revascularization.

Background: Evidence is emerging to support the concept that the failing heart is "energy depleted" and that defects in energy metabolism are important determinants in the development and the progression of the disease. We have shown previously that depressed mitochondrial function in cardiac and skeletal muscles in chronic heart failure is linked to decreased expression of the gene encoding transcriptional proliferator-activated receptor-gamma coactivator-1alpha, the inducible regulator of mitochondrial biogenesis and its transcription cascade, leading to altered expression of mitochondrial proteins. However, oxidative capacity of the myocardium of patients treated for chronic heart failure and pathophysiological mechanisms of mitochondrial dysfunction are still largely unknown., Methods and Results: In patients with chronic heart failure treated with angiotensin-converting enzyme inhibition, cardiac oxidative capacity, measured in saponin-permeabilized fibers, was 25% lower, and proliferator-activated receptor-gamma coactivator-1alpha protein content was 34% lower compared with nonfailing controls. In a rat model of myocardial infarction, angiotensin-converting enzyme inhibition therapy was only partially able to protect cardiac mitochondrial function and transcription cascade. Expression of proliferator-activated receptor-gamma coactivator-1alpha and its transcription cascade were evaluated after a 48-hour exposure of cultured adult rat ventricular myocytes to endothelin-1, angiotensin II, aldosterone, phenylephrine, or isoprenaline. Endothelin-1 (-30%) and, to a lesser degree, angiotensin II (-20%) decreased proliferator-activated receptor-gamma coactivator-1alpha mRNA content, whereas other hormones had no effect (phenylephrine) or even increased it (aldosterone, isoprenaline)., Conclusions: Taken together, these results show that, despite angiotensin-converting enzyme inhibition treatment, oxidative capacity is reduced in human and experimental heart failure and that endothelin-1 and angiotensin II could be involved in the downregulation of the mitochondrial transcription cascade.

The iron deficiency is a major problem of public health in the African countries, particularly in pregnant women population. The aim of our study was to appreciate the iron status during the pregnancy period (first, second and three trimesters); to realize an evaluation and to characterize the biological indicators of pregnant women. Our study was carried out in four medical and urban units of Abidjan in Côte-d'Ivoire with 531 pregnant women. The biological parameters significantly reduced in the third trimester of the pregnancy. But, an enhancement of the transferrin and the total iron binding capacity was observed. Moreover, 66 % of pregnant women presented iron deficiency anaemia (p < 0.01). In conclusion, the study shows that no pregnant woman presented iron normal status in the third trimester of the pregnancy.

Heart failure is associated with alterations in cardiac and skeletal muscle energy metabolism resulting in a generalized myopathy. We investigated the molecular and cellular effects of angiotensin-converting enzyme inhibition (ACEi) on skeletal muscle metabolism in infarcted animals. Myocardial infarction (MI) was obtained by left descending coronary artery ligation. Sham, MI, and MI-treated rats (perindopril, 2 mg.kg(-1).day(-1) given 7 days after MI) were studied 1 and 4 mo after surgery. Oxygen consumption of white gastrocnemius (Gas) muscle was studied in saponin-permeabilized fibers, using the main substrates of mitochondrial respiration. mRNA expression of nuclear factors (PGC-1alpha, NRF-2alpha, and mtTFA), involved in the transcription of mitochondrial proteins, and of MCIP1, a marker of calcineurin activation, were also determined. Echocardiographic left ventricular fractional shortening was reduced in both MI and perindopril group after 1 and 4 mo, whereas systemic blood pressure was reduced by 16% only in the MI group after 4 mo. The capacity of Gas to oxidize glutamate-malate, glycerol-triphosphate, or pyruvate (-30%, P < 0.01; -32%, P < 0.05; -33%, P < 0.01, respectively), was greatly decreased. Furthermore, PGC-1alpha (-54%), NRF-2alpha (-45%), and MCIP1 (-84%) gene expression were significantly downregulated. ACEi improved survival, left ventricular function, and blood pressure. Perindopril protected also totally the Gas mitochondrial function and preserved the mRNAs concentration of the mitochondrial transcriptional factors. Moreover, PGC-1alpha correlated with Gas oxidative capacity (r = 0.48), mitochondrial cytochrome-c oxidase (r = 0.65), citrate synthase (r = 0.45) activities, and MCIP1 expression (r = 0.44). Thus ACEi totally prevented MI-induced alterations of skeletal muscle mitochondrial function and protein expression, halting the development of this metabolic myopathy.

The responsiveness of mature regenerated soleus (SOL) muscles to cyclosporin A (CsA) administration was studied in rats. Forty-two days after notexin-induced degeneration of left SOL muscles, rats were treated with CsA (25 mg/kg x day) or vehicle daily for 3 weeks. CsA administration decreased by eightfold the level of transcription of MCIP-1, a well-known calcineurin-induced gene, in intact as well as in regenerated muscles (P < 0.001). In response to CsA-administration we observed a slow-to-fast transition in the MHC profile, more marked in regenerated than in intact muscles (P < 0.05), but mainly restricted to MHC-Ibeta toward MHC-IIA. Immunohistochemical analysis showed that MHC-IIA was often co-expressed with MHC-Ibeta within myofibers of intact muscles, whereas it was mainly expressed within pure fast fibers of regenerated muscles. MHC-Ibeta mRNA levels were lower in regenerated than in intact muscles, but did not change in response to CsA-administration. CsA administration induced a significant increase in MHC-IIA mRNA levels (P < 0.001) similar in both intact and regenerated muscles. Present results suggest that in vivo in intact SOL muscles, calcineurin blocks the upregulation of the MHC-IIA isoform at the transcriptional level. On the other hand, the higher response of regenerated muscles to CsA administration cannot be explained by transcriptional events, and may result from either a more rapid turnover of MHC proteins in regenerated muscles than in intact ones, or translational events. This study further suggests that the developmental history of myofibers could play a role in the adaptability of skeletal muscle to variations in neuromuscular activity., (Copyright 2006 Wiley-Liss, Inc.)

This study investigates whether adaptations of mitochondrial function accompany the improvement of endurance performance capacity observed in well-trained athletes after an intermittent hypoxic training program. Fifteen endurance-trained athletes performed two weekly training sessions on treadmill at the velocity associated with the second ventilatory threshold (VT2) with inspired O2 fraction = 14.5% [hypoxic group (Hyp), n = 8] or with inspired O2 fraction = 21% [normoxic group (Nor), n = 7], integrated into their usual training, for 6 wk. Before and after training, oxygen uptake (VO2) and speed at VT2, maximal VO2 (VO2 max), and time to exhaustion at velocity of VO2 max (minimal speed associated with VO2 max) were measured, and muscle biopsies of vastus lateralis were harvested. Muscle oxidative capacities and sensitivity of mitochondrial respiration to ADP (Km) were evaluated on permeabilized muscle fibers. Time to exhaustion, VO2 at VT2, and VO2 max were significantly improved in Hyp (+42, +8, and +5%, respectively) but not in Nor. No increase in muscle oxidative capacity was obtained with either training protocol. However, mitochondrial regulation shifted to a more oxidative profile in Hyp only as shown by the increased Km for ADP (Nor: before 476 +/- 63, after 524 +/- 62 microM, not significant; Hyp: before 441 +/- 59, after 694 +/- 51 microM, P < 0.05). Thus including hypoxia sessions into the usual training of athletes qualitatively ameliorates mitochondrial function by increasing the respiratory control by creatine, providing a tighter integration between ATP demand and supply.

We performed repeated analysis of mitochondrial respiratory function in skeletal muscle (SM) of patients with early-stage sporadic amyotrophic lateral sclerosis (SALS) to determine whether mitochondrial function was altered as the disease advanced. SM biopsies were obtained from 7 patients with newly diagnosed SALS, the same 7 patients 3 months later, and 7 sedentary controls. Muscle fibers were permeabilized with saponin, then skinned and placed in an oxygraphic chamber to measure basal and maximal adenosine diphosphate (ADP)-stimulated respiration rates and to assess mitochondrial regulation by ADP. We found that the maximal oxidative phosphorylation capacity of muscular mitochondria significantly increased, and muscular mitochondrial respiratory complex IV activity significantly decreased as the disease advanced. This temporal study demonstrates for the first time that mitochondrial function in SM in human SALS is progressively altered as the disease develops.

We examined the transcriptional signaling cascade involved in the changes of mitochondrial biogenesis and mitochondrial function of skeletal muscle and of the exercise capacity of humans in response to long-term physical activity and chronic heart failure (CHF). Biopsy samples of vastus lateralis muscle were obtained from 18 healthy subjects with different fitness levels (assessed by maximal oxygen uptake, VO2 peak). We compared 9 sedentary subjects with 10 CHF patients undergoing transplantation. Muscle oxidative capacity was measured in permeabilized fibers (Vmax). Transcript levels of target genes were quantified by RT-PCR. In healthy subjects, VO2 peak was linearly related to Vmax (P<0.01) and to the gene expression of mitochondrial proteins and of the coactivator PGC-1alpha and its downstream transcription factors. A coordinate increase in PGC-1alpha and mRNA levels of proteins involved in degradation, fusion, and fission of mitochondria was observed associated with calcineurin activation. Despite decreased VO2 peak, in CHF patients skeletal muscles showed preserved Vmax in accordance with preserved markers and transcription factors of mitochondrial biogenesis and dynamics, with no calcineurin activation. The results provide strong support for a central role for PGC-1alpha and calcineurin activation in mitochondrial biogenesis in healthy and diseased human skeletal muscles.

While the divisions of the facial nerve in the face are well known, the innervation of the orbicularis oculi by the different distal branches of the facial nerve is poorly described. To determine which branches of the facial nerve play a role in this innervation, the facial nerve was dissected in 30 fresh cadavers. The innervation of this muscle was in the form of two plexuses, a superior one, most often (93%) formed by the union of the temporal and superior zygomatic branches, and an inferior one, usually formed (63%) by the union of the inferior zygomatic and superior buccal branches. This new mode of innervation explains how, without damage to both plexuses, innervation of orbicularis oculi by the facial nerve remains functional. It also explains the often unsatisfactory results of treatment of primary blepharospasm, and the unusual character of palsies of this muscle in cervicofacial lifts.

Techniques and protocols of assessment of mitochondrial properties are of physiological and physiopathological important significance. A precise knowledge of the advantages and limitations of the different protocols used to investigate the mitochondrial function, is therefore necessary. This report presents examples of how the skinned (or permeabilized) fibers technique could be applied for the polarographic determination of the actual quantitative and qualitative aspects of mitochondrial function in human muscle samples. We described and compared the main available respiration protocols in order to sort out which protocol seems more appropriate for the characterization of mitochondrial properties according to the questions under consideration: quantitative determination of oxidative capacities of a given muscle, characterization of the pattern of control of mitochondrial respiration, or assessment of a mitochondrial defect at the level of the respiratory chain complexes. We showed that while protocol A, using only two levels of the phosphate acceptor adenosine diphosphate (ADP) concentration and the adjunction of creatine, could be used for the determination of quantitative changes in very small amount of muscle samples, the ADP sensitivity of mitochondrial respiration was underestimated by this protocol in muscles with high oxidative capacities. The actual apparent Km for ADP and the role of functional activation of miCK in ATP production and energy transfer in oxidative muscles, are well-assessed by protocol B (in the absence of creatine) together with protocol C (in the presence of creatine) that use increasing concentrations of ADP ranging from 2.5-2000 microM. Protocol D is well-adapted to investigate the potential changes at different levels of the respiratory chain, by the use of specific substrates and inhibitors. As can be seen from the present data and the current review of previous reports in the literature, a standardization of the respiration protocols is needed for useful comparisons between studies.

Previous studies suggested that administration of cyclosporin A (CsA), an immunosuppressive agent, contributes to the increased fatigability of heart transplant recipients. The aim of this study was to investigate whether CsA itself, without vehicle, affects the function of mitochondria maintained in situ, in rats treated with CsA (25mg/kg/day) dissolved in ethanol and olive oil. Treatment with CsA induced a 16% decrease in slow myosin heavy chain (MHC) associated with a 225% increase in fast MHCIIa. The proportion of fibers expressing type IIa MHC increased as a result of CsA treatment. Soleus from the CsA-treated animals showed an increase in both basal (+85%) and maximal (+37%) mitochondrial respiration (P < 0.001), consistent with a 24% increase in citrate synthase activity, whereas the apparent Km for adenosine diphosphate was unchanged. By itself, CsA has no deleterious effects on muscle oxidative capacity but induces alterations in energy metabolism in accordance with the increased proportion of fast-twitch oxidative fibers.

Objectives: We sought to determine whether intrinsic mitochondrial function and regulation were altered in heart transplant recipients (HTRs) and to investigate the response of mitochondrial function to six-week endurance training in these patients., Background: Despite the normalization of central oxygen transport during exercise, HTRs are still characterized by limited exercise capacity, which is thought to result from skeletal muscle metabolic abnormalities., Methods: Twenty HTRS agreed to have vastus lateralis biopsies and exercise testing: before and after training for 12 of them and before and after the same control period for eight subjects unwilling to train. Mitochondrial respiration was evaluated on saponin-permeabilized muscle fibers in the absence or presence (maximum respiration rate [V(max)]) of saturating adenosine diphosphate., Results: Mitochondrial function was preserved at the level of sedentary subjects in untrained HTRs, although they showed 28 +/- 5% functional aerobic impairment (FAI). After training, V(max), citrate synthase, cytochrome c oxidase, and mitochondrial creatine kinase (CK) activities were significantly increased by 48%, 40%, 67%, and 53%, respectively (p < 0.05), whereas FAI decreased to 12 +/- 5% (p < 0.01). The control of mitochondrial respiration by creatine and mitochondrial CK was also improved (p < 0.01), suggesting that phosphocreatine synthesis and transfer by the mitochondrial CK become coupled to oxidative phosphorylation, as shown in trained, healthy subjects., Conclusions: In HTRs, the mitochondrial properties of skeletal muscle were preserved and responded well to training, reaching values of physically active, healthy subjects. This suggests that, in HTRs, immunosuppressive drugs do not alter the intrinsic muscle oxidative capacities and that the patients' physical handicap results from nonmitochondrial mechanisms.

In chronic obstructive pulmonary disease, inspiratory muscles face increased resistive and elastic workloads and therefore increased energy requirements. The adaptive response of these muscles to this higher energy demand includes increased oxidative enzymes and changes in contractile protein expression but the consequences on mitochondrial function and energy metabolism have not been assessed so far. We investigated the in situ properties of the mitochondria of costal diaphragm and external intercostal muscles using the skinned fiber technique in 9 emphysematous and 11 age-matched control patients. Biopsies obtained during thoracic surgery were placed in an oxygraphic chamber to measure maximal oxygen uptake. We observed that the maximal oxidative capacity of diaphragm and external intercostal muscles increased significantly in the emphysematous group compared with the control group (+135 and +37%, respectively). Significant correlations were found between the maximal oxidative capacity and patients' pulmonary indexes of obstruction (diaphragm: r = -0.637, intercostal: r = -0.667, p < 0.005) and hyperinflation (diaphragm: r = 0.639, p < 0.003, intercostal: r = 0.634, p < 0.01). Slow myosin heavy chain isoform increased in the diaphragm of the emphysematous group, with significant relationships between indexes of obstruction and hyperinflation and activities of biochemical mitochondrial markers. Thus, severe emphysema was associated with increased mitochondrial capacity and efficiency in the inspiratory muscles, supporting an endurance training-like effect.

Objective: Mitochondrial function and metabolic profile of slow and fast skeletal muscles and cardiac muscle are altered in chronic heart failure (CHF), suggesting a generalized metabolic myopathy in this disease. The aim of this study was to investigate the potential beneficial effects of voluntary activity on cardiac and skeletal muscle energetics in heart failure., Methods: Heart failure was induced in rats by aortic stenosis. Four months after surgery, part of sham and CHF animals were randomly assigned to activity cages equipped with running wheels for 8 weeks or kept sedentary. Mitochondrial capacity and regulation were measured using saponin skinned fibers in left ventricle, slow and fast skeletal muscles, and metabolic and myosin profiles were established., Results: Despite four times lower performances of CHF rats, alterations in metabolic and myosin parameters (oxidative capacity, mitochondrial enzymes, cytosolic and mitochondrial creatine kinase, myosin heavy chains) observed in all muscles of CHF animals were almost fully restored in soleus muscle though unchanged in heart and fast skeletal muscles., Conclusions: These results show the powerful beneficial effect of physical activity specifically on active slow oxidative skeletal muscle in CHF, without the worsening of cardiac muscle metabolism.

This study explores the importance of creatine kinase (CK) in the regulation of muscle mitochondrial respiration in human subjects depending on their level of physical activity. Volunteers were classified as sedentary, active or athletic according to the total activity index as determined by the Baecke questionnaire in combination with maximal oxygen uptake values (peak V(O2), expressed in ml min(-1) kg(-1)). All volunteers underwent a cyclo-ergometric incremental exercise test to estimate their peak V(O2) and V(O2) at the ventilatory threshold (VT). Muscle biopsy samples were taken from the vastus lateralis and mitochondrial respiration was evaluated in an oxygraph cell on saponin permeabilised muscle fibres in the absence (V(0)) or in the presence (V(max)) of saturating [ADP]. While V(0) was similar, V(max) differed among groups (sedentary, 3.7 +/- 0.3, active, 5.9 +/- 0.9 and athletic, 7.9 +/- 0.5 micromol O2 min(-1) (g dry weight)(-1)). V(max) was correlated with peak V(O2) (P < 0.01, r = 0.63) and with V(T) (P < 0.01, r = 0.57). There was a significantly greater degree of coupling between oxidation and phosphorylation (V(max)/V(0)) in the athletic individuals. The mitochondrial K(m) for ADP was significantly higher in athletic subjects (P < 0.01). Mitochondrial CK (mi-CK) activation by addition of creatine induced a marked decrease in K(m) in athletic individuals only, indicative of an efficient coupling of mi-CK to ADP rephosphorylation in the athletic subjects only. It is suggested that increasing aerobic performance requires an enhancement of both muscle oxidative capacity and mechanisms of respiratory control, attesting to the importance of temporal co-ordination of energy fluxes by CK for higher efficacy.