Small Muscle Groups Research Articles

Effects of Sodium Bicarbonate Supplementation on Muscular Strength and Endurance: A Systematic Review and Meta-analysis.

The effects of sodium bicarbonate on muscular strength and muscular endurance are commonly acknowledged as unclear due to the contrasting evidence on the topic. To conduct a systematic review and meta-analysis of studies exploring the acute effects of sodium bicarbonate supplementation on muscular strength and endurance. A search for studies was performed using five databases. Meta-analyses of standardized mean differences (SMDs) were performed using a random-effects model to determine the effects of sodium bicarbonate supplementation on muscular strength (assessed by changes in peak force [N], peak torque [Nm], or maximum load lifted [kg]) and muscular endurance (assessed by changes in the number of repetitions performed, isokinetic total work, or time to maintain isometric force production). Subgroup meta-analyses were conducted for the muscular endurance of small vs. large muscle groups and muscular strength tested in a rested vs. fatigued state. A random-effects meta-regression analysis was used to explore possible trends in the effects of: (a) timing of sodium bicarbonate ingestion; and (b) acute increase in blood bicarbonate concentration (from baseline to pre-exercise), on muscular endurance and muscular strength. Thirteen studies explored the effects of sodium bicarbonate on muscular endurance and 11 on muscular strength. Sodium bicarbonate supplementation was found to be ergogenic for muscular endurance (SMD = 0.37; 95% confidence interval [CI]: 0.15, 0.59; p = 0.001). The performance-enhancing effects of sodium bicarbonate were significant for both small (SMD = 0.31; 95% CI: 0.04, 0.59; p = 0.025) and large muscle groups (SMD = 0.40; 95% CI: 0.13, 0.66; p = 0.003). Sodium bicarbonate ingestion was not found to enhance muscular strength (SMD = - 0.03; 95% CI: - 0.18, 0.12; p = 0.725). No significant effects were found regardless of whether the testing was carried out in a rested (SMD = 0.02; 95% CI: - 0.09, 0.13; p = 0.694) or fatigued (SMD = - 0.16; 95% CI: - 0.59, 0.28; p = 0.483) state. No significant linear trends in the effects of timing of sodium bicarbonate ingestion or acute increase in blood bicarbonate concentrations on muscular endurance or muscular strength were found. Overall, sodium bicarbonate supplementation acutely improves muscular endurance of small and large muscle groups, but no significant ergogenic effect on muscular strength was found.

Hemodynamic responses to strength exercise with blood flow restriction in small muscle groups

The aim of this study was to analyze the acute hemodynamic responses to strength exercise with blood flow restriction involving small muscle groups. The sample consisted of 10 male volunteers (22.6 ± 2.07 years, 1.78 ± 0.06 m, 76.32 ± 13.36 kg) who randomly performed two experimental protocols involving the elbow flexion exercise with the dominant arm: strength exercise of the elbow flexors with blood flow restriction (EFBFR) and strength exercise of the elbow flexors without blood flow restriction (EEF). A cross-over design with a seven to ten days interval between the experimental protocols was used. Systolic blood pressure (SBP), diastolic (DBP) and mean (MAP), pulse pressure (PP), heart rate (HR) and double product (DP) were evaluated at rest, immediately after exercise and at 15 minutes of recovery. SBP, DBP and MAP presented a significant increase (p <0.05) immediately after EFBFR when compared to the protocol without blood flow restriction, returning to rest values at the 15 minutes of recovery. DBP significantly reduced (p <0.05) in the recovery period only in the EFBFR experiment and HR increased post-effort in both experiments. The PP and DP did not change between the different times, regardless of the protocol.The results of the present study allow us to conclude that strength exercise with BFR involving small muscle groups was more efficient than exercise without BFR to promote acute changes in hemodynamic responses and that BFR did not represent a cardiovascular risk considering its effects on PP.

Hemodynamic responses to strength exercise with blood flow restriction in small muscle groups

Hemodynamic responses to strength exercise with blood flow restriction in small muscle groups

Effect of Autonomic Responses After Isometric Training at Different Intensities on Obese People.

Arterial hypertension is among the leading causes of mortality worldwide. The primary non-pharmacological management of arterial hypertension is isometric grip training, which has shown better results than pharmacological methods; however, it has not been thoroughly studied in large muscle groups. This study compared the pressor response of isometric exercise training at different intensities, in large groups versus small muscle groups, in sedentary eutrophic and overweight people aged 20-29 years. A sample of 93 people (57 people with excess weight and 36 people of normal weight) participated in isometric training for 5 days, subdivided into leg press vs. handgrip strength, with different intensities for each subgroup (30 and 50%, 1 RM). Before and after the 5 training days, Heart Rate Variability (HRV) and systolic and diastolic blood pressure, BSBP-BDBP and PSBP-PDBP, were measured to evaluate the state of sympathetic activation at rest and pressor response. Changes with significant differences (p <0.05) in terms of pre-post training measurements in the eutrophic group were the BSBP-PSBP variables at 30% and 50% 1 RM for manual isometric grip strength. In the excess weight group, the only significant change was the PSBP variable in handgrip strength at 30% 1 RM. It should be noted that in all cases, blood pressure values reduced. Isometric strength exercises in large and small muscle groups show a tendency to reduce blood pressure values; however, the isometric handgrip force at 30% 1 RM shows statistically significant reductions in blood pressure values.

MUSCLE STRENGTH AND CAFFEINE SUPPLEMENTATION: ARE WE DOING MORE OF THE SAME?

ABSTRACT The purpose of this review was to examine in the current literature the advances made in terms of the effects of caffeine supplementation on maximum strength and its associated mechanisms since the publication of two important papers in 2010. Searches were carried out in the PubMed, Medline, Scielo and Web of Science databases for articles published after 2010. Sixteen studies were included based on inclusion and exclusion criteria. Five studies did not report changes in maximal voluntary strength (31.3%). Four of them used isometric muscle contractions, although this may not be a key factor because five other studies also used isometric contractions and reported ergogenic effects. Furthermore, these four studies evaluated small muscle groups and volunteers were not accustomed to consuming caffeine. Caffeine produced ergogenic effects in eleven of the sixteen studies analyzed (68.8%). None of the doses were clearly related to ergogenic effects; however, a dose of at least 3 mg/kg of caffeine is probably necessary. Caffeine ergogenicity was affected by various factors. There was a lack of standardized protocols and controls for intervening factors (e.g., circadian cycles and nutritional states), which could affect results. An ideal caffeine supplementation protocol that is useful for future research, athletes, and physical activity practitioners, has yet to be defined. A small advance made since 2010 involved a possible lack of gender difference; it would appear that caffeine supplementation affects men and women equally. Level of Evidence I; Systematic Review of Level I Studies.

Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis.

Citrulline is an increasingly common dietary supplement that is thought to enhance exercise performance by increasing nitric oxide production. In the last 5years, several studies have investigated the effects of citrulline supplements on strength and power outcomes, with mixed results reported. To date, the current authors are unaware of any attempts to systematically review this emerging body of literature. The current study sought to conduct a systematic review and meta-analysis of the literature describing the effects of citrulline supplementation on strength and power outcomes. A comprehensive, systematic search of three prominent research databases was performed to find peer-reviewed, English language, original research studies evaluating the effects of citrulline supplementation on indices of high-intensity exercise performance in healthy men and women. Outcomes included strength and power variables from performance tests involving multiple repetitive muscle actions of large muscle groups, consisting of either resistance training sets or sprints lasting 30s or less. Tests involving isolated actions of small muscle groups or isolated attempts of single-jump tasks were not included for analysis due to differences in metabolic requirements. Studies were excluded from consideration if they lacked a placebo condition for comparison, were carried out in clinical populations, provided a citrulline dose of less than 3g, provided the citrulline dose less than 30min prior to exercise testing, or combined the citrulline ingredient with creatine, caffeine, nitrate, or other ergogenic ingredients. Twelve studies, consisting of 13 total independent samples (n = 198 participants), met the inclusion criteria. Between-study variance, heterogeneity, and inconsistency across studies were low (Cochrane's Q = 6.9, p = 0.86; τ2 = 0.0 [0.0, 0.08], I2 = 0.0 [0.0, 40.0]), and no funnel plot asymmetry was present. Results of the meta-analysis identified a significant benefit for citrulline compared to placebo treatments (p = 0.036), with a small pooled standardized mean difference (SMD; Hedges' G) of 0.20 (95% confidence interval 0.01-0.39). The effect size was small (0.20), and confidence intervals for each individual study crossed the line of null effect. However, the results may be relevant to high-level athletes, in which competitive outcomes are decided by small margins. Further research is encouraged to fully elucidate the effects of potential moderating study characteristics, such as the form of citrulline supplement, citrulline dose, sex, age, and strength versus power tasks.

Застосування адаптивної фізичної культури у відновленні компенсаторних функцій хребта при остеохондрозі у осіб другого зрілого віку

The restoration of the compensatory functions of the spine in osteochondrosis in the elderly is a pressing issue in both medicine and physical rehabilitation. Almost half of the persons of the second period of mature age suffer from osteochondrosis of the spine, which leads to pain, muscle contractions, a decrease in the amplitude of movement, and the like. That is why the need for the application of special methods of physical rehabilitation to restore vital functions. Based on the analysis and synthesis of scientific medical literature and physical education and sports, an experimental technique has been developed to actively restore the spinal compensatory functions in osteochondrosis of the spine in the elderly. The method is based on the use of methods of adaptive physical culture as a set of measures, including exercise therapy and therapeutic massage. Spinal osteochondrosis is a degenerative process, in which there may be subluxations in the vertebral joints or slipping of the vertebrae is observed, as a result of which the spinal cord and its roots are injured. Use in the elderly, patients with osteochondrosis of the spine, experimental methods of active recovery of the compensatory functions of the spine gave a positive dynamic of functional changes. The experimental methodology is based on the application of adaptive physical culture methods as a set of measures that include exercise therapy and therapeutic massage. An experimental procedure for the active restoration of compensatory functions of the spine with osteochondrosis has been developed, which is based on: exercises for relaxation of the muscles of the upper extremities, shoulder girdle; unloading of the affected division of the spine; relaxation exercises; exercises for small and medium muscle groups; corrective exercises; breathing exercises static and dynamic. It is proved that taking special exercises, dispensing them, depending on the nature and clinical course of the disease, can purposefully affect and mainly change certain functions of the body by restoring damaged systems, adapting the patient to the physical load of domestic and industrial nature. Evaluation of the effectiveness of the method of active restoration of compensatory functions of the spine in osteochondrosis included the definition of appropriate criteria, which include: mobility of the intervertebral joints; the dynamics of pain syndrome; research of psychoemotional manifestations. The results of experimental studies have shown positive dynamics in the experimental group of the elderly, patients with spinal osteochondrosis, in connection with adaptation to physical activity and increase their motor activity. The testing of mental functions showed a positive effect of the experimental complex of exercises on the emotional state of patients.

Ordem do treinamento com pesos, capacidade funcional e carga de treino em idosos treinados: ensaio clínico aleatorizado.

Introdução: a ordem do treinamento com pesos (TP) pode estar relacionada aos benefícios observados nesta modalidade. Objetivo: avaliar a ordem de TP na capacidade funcional e carga de treino. Métodos: dezoito idosos treinados foram aleatorizados: sequência A (SEQ A), dos grandes para os pequenos grupos musculares e sequência B (SEQ B), ordem inversa a SEQ A. A flexibilidade, tarefas funcionais, resistência muscular e carga de treino foram verificados. Resultados: interação foi observada para a flexibilidade, em que a SEQ B (+ 18,7%) apresentou resultado significativo, quando comparada à SEQ A (- 18,4%). Efeito do tempo foi encontrado para tarefa funcional (SEQ A = - 2,9% e SEQ B = - 1,9%), resistência muscular (SEQ A = + 11,5% e SEQ B = + 8,9%) e carga de treino (SEQ A = + 54,0% e SEQ B = + 74,3%). Conclusão: TP é efetivo para a melhora da tarefa funcional, da resistência muscular e da carga de treino, porém a ordem pode influenciar na flexibilidade.

Digital Human Models in Human Factors and Ergonomics Evaluation of Gesture Interfaces

Gesture-based interfaces are becoming a widely used interaction modality in many industrial applications. Therefore, it is important to guarantee usable and ergonomic interfaces for workers. The purpose of this study was to investigate whether the use of digital human models (DHMs) by human factors/ergonomics (HFE) experts can complement the user evaluation of gesture interface prototypes. Two case studies were conducted, in which gesture-based systems for remote robot control were evaluated. The results indicate that the use of DHMs supports the findings from self-reported HFE evaluations. However, digital human modeling still has some limitations. For example, in this study, it was not possible to evaluate small muscle groups (e.g. fingers). We argue that adaptation of the DHMs could be a rapid and simple alternative for supporting the HFE design of gestures.

Loads on small muscle groups as a risk of hypertensive conditions

Loads on small muscle groups as a risk of hypertensive conditions

Functional electrical stimulation-induced muscular fatigue: Effect of fiber composition and stimulation frequency on rate of fatigue development

This investigation evaluated the progression towards fatigue in two muscles of differing fast- and slow-twitch fiber proportions (abductor pollicis brevis (APB) and vastus lateralis (VL)) when activated by functional electrical stimulation (FES) at three frequencies (10, 35, and 50 Hz). Fatigue was defined as a 50% drop from the initial FES-induced force of 25% maximal voluntary contraction (MVC). Ten healthy adults (mean age: 23.2 ± 3.0 years) were recruited; participants signed an IRB approved consent form prior to participation. Protocols were developed to evaluate the effects of muscle size, fiber type and FES frequency on total time to fatigue. Results indicated that the predominantly fast-twitch VL fatigued more quickly than the slow-twitch APB at the higher frequencies (p < 0.05), but did not significantly differ with stimulation at 10 Hz. Overall, muscle size and FES frequencies showed some significant interactions when generating a defined force and during fatigue development. Furthermore, it appears that to reduce fatigue, FES treatments should not extend past ∼14–16 min for large and small muscle groups, respectively, when the muscle group’s optimal stimulation frequency is applied.

Reactive Oxygen Species as Agents of Fatigue.

For more than three decades, muscle biologists have been fascinated by reactive oxygen species (ROS) generated in exercising muscle and the potential role that ROS may play in fatigue. Reports in the peer-reviewed literature were analyzed and published findings integrated to synthesize an overview of ROS as agents of fatigue. Muscle tissue contains multiple sources of ROS, and specific ROS molecules have been detected in muscle, including superoxide anions, hydrogen peroxide, and hydroxyl radicals. These species are present throughout the tissue, i.e., myofiber organelles and cytosol, extracellular space, and intravascular compartment, and ROS concentrations increase during strenuous contractions. Direct ROS exposure evokes many of the same changes that occur in muscle during fatigue, suggesting a possible relationship. The hypothesis that ROS play a causal role in fatigue has been tested extensively, a large body of data have been compiled, and the once-controversial verdict is now in: ROS accumulation in working muscle clearly contributes to the loss of function that occurs in fatigue. This is evident in a range of experimental settings ranging from muscle fiber bundles in vitro to neuromuscular preparations in situ, from volitional exercise of small muscle groups to whole-body exercise by elite athletes. The robust capacity of antioxidant pretreatment to delay fatigue provides compelling evidence that ROS play a causal role in this process. There are caveats to this story of course, issues related to the type of antioxidant and mode of administration. Also, the translation of this laboratory concept into clinical practice has been slow. Still, antioxidant therapy has the potential to benefit individuals who experience premature fatigue and this remains a promising area for future research.

Editorial: A Hand at Work: Effects of Aging.

Editorial: A Hand at Work: Effects of Aging.

Effect of Exercise Order of Resistance Training on Strength Performance and Indices of Muscle Damage in Young Active Girls.

BackgroundExercise order is one of the key variables in designing resistance training (RT) that may affect physiological and functional muscle characteristics.ObjectivesThe purpose of this research was to examine the effect of exercise order of RT on muscle strength, lactate dehydrogenase (LDH) and creatine kinase (CK) enzymes as indices of muscle damage in active young girls.Patients and MethodsFor this purpose, 24 active girls aged 20 - 30 years voluntarily participated in six weeks RT. The subjects were randomly assigned into three groups of large to small muscle group (SLM, n = 8), large to small group (LSM, n = 8) and control group (Co, n = 8). The RT performed in bench press, lat pull down, triceps with machine and biceps with barbell. Before and after RT, blood sample was collected to measure the level of LDH and CK enzymes activity.ResultsThe result of analysis indicated that RT significantly increased the level of LDH enzymes in all three groups (P < 0.05). In addition, the result showed that six weeks of RT did not cause any significant change in CK (P > 0.05). However, there is no significant difference between SLM, LSM and control in CK and LDH after six weeks RT.ConclusionsBoth RT methods cause the same improvement on muscle strength and performance. Also muscle damage indices did not show sensitivity to the exercise order. Therefore, resistance training may be designed regardless of effect of exercise order on muscle damage.

Comparison of the Effects of Resistance Exercise Orders on Number of Repetitions, Serum IGF-1, Testosterone and Cortisol Levels in Normal-Weight and Obese Men

Background:Exercise order affects repetition performance and acute hormonal responses to resistance training (RT) programs.Objectives:The purpose of this study was to compare the acute effects of two different resistance exercise orders (REO) on number of repetitions and serum Insulin-like Growth Factor-1 (IGF-1), testosterone and cortisol levels in normal-weight and obese men.Materials and Methods:25 untrained college-aged men were assigned to either obese (n = 11) or normal-weight (n = 15) groups. Subjects performed two REO protocols in 2 exercise groups. In the first group subjects began with large-muscle group and progressed to small-muscle group (Protocol A), while in the other group subjects performed the same exercise but in reverse sequence (Protocol B). Each activity was performed in 3 consecutive sets of 10 repetitions maximum to near fatigue.Results:REOs did not affect number of repetitions in none of the groups. The average rating of perceived exertion was higher for protocol B in both groups. IGF-1 and testosterone increased immediately post exercise for both protocols and in both groups, however immediately post exercise increase in IGF-1 and testosterone were lower in obese group. Cortisol response to REO was weaker in obese group.Conclusions:Performing large muscle group exercises first in RE training and progressing to small muscle group produced greater anabolic hormonal response relative to reverse sequence in normal-weight young adult men. Anabolic hormonal response to REOs was blunted in the obese group.

Posture and Helmet Load Influences on Neck Muscle Activation.

Night vision goggles (NVG) are linked to increased neck muscle activation and pain. Counterweights (NVGcw) are hypothesized to mitigate these effects. The purpose of this study was to investigate the muscular response to varying helmet loads and postures. Volunteering from a representative squadron were 16 male helicopter aviators (pilots, N = 9; flight engineers, N = 7). Subjects performed head movements to assume nine different postures (three directions: left, center, and right, at three different levels: down, level, and up) with four different head loads (no helmet; helmet only; NVG; and NVGcw) in randomized order. Subjects were provided real time visual guidance and feedback while assuming the appropriate posture in a cockpit seat in a laboratory setting. Neck muscle activation was assessed with electromyography (EMG) of four different muscle groups, bilaterally, including the sternocleidomastoid, splenius capitis, and mid and lower trapezius. Two- to fourfold increases in muscle activation were observed in postures to the left (down, level, and up) while subjects wore either the NVG or NVGcw as compared to the baseline of no helmet. This was most prevalent in smaller muscle groups (i.e., the sternocleidomastoid and splenius capitis) as compared to larger muscle groups (i.e., the mid and lower trapezius). The use of NVGcw did not decrease neck muscle activity as compared to NVG only, particularly when the head posture moved the field of view below the horizon. This suggests interventions to decrease neck muscle activity and fatigue in military helicopter aircrew using NVG should focus on task specific guidelines with respect to countermeasures.

Acute Effects of Low-Load/High-Repetition Single-Limb Resistance Training in COPD.

To investigate the acute effects of partitioning exercise on exercise workload, exertional symptoms and quadriceps muscle fatigue during low load/high-repetition resistance exercises in people with COPD and healthy controls. We compared the acute physiological effects of single-limb (SL) versus two-limb (TL) execution of isokinetic knee extension and of six low load/high-repetition elastic resistance exercises in 20 people with COPD (forced expiratory volume in 1 s = 38% predicted) and 15 healthy controls. Among people with COPD, SL exercises resulted in higher exercise workloads during isokinetic knee extension (17% ± 31%, P < 0.05) and elastic exercises (rowing, 17% ± 23%; leg curl, 23% ± 21%; elbow flexion, 19% ± 26%; chest press, 14% ± 15%; shoulder flexion, 33% ± 24%; and knee extension, 24% ± 18%, all P < 0.05). Muscle fatigue ratings were similar during SL compared with TL exercises, whereas dyspnea ratings were similar between conditions during isokinetic exercises and lower during SL compared with TL elastic exercises (P < 0.05). In COPD, SL knee extension resulted in greater quadriceps fatigue than TL knee extension as evidenced by a greater fall in quadriceps potentiated twitch force after the former exercise (-24% ± 10% vs -16% ± 8%, P = 0.025). In healthy controls, partitioning exercise with SL exercise did not modify workload, quadriceps fatigue nor dyspnea achieved during the various exercises. Partitioning exercise by exercising using an SL allowed higher muscle localized exercise workloads, larger amount of quadriceps muscle fatigue with lower, or similar level of exertional symptoms during low load/high-repetition resistance exercises in people with advanced COPD.

Determination of aerobic–anaerobic transition in the working muscle using EMG and near-infrared spectroscopy data

A method to evaluate aerobic-anaerobic transition (AAT) during exercise is suggested. The subjects performed two tests with incremental increase of load: bicycle exercise and one leg knee extensions. In both tests the relation of deoxygenated hemoglobin (HHb) to EMG-activity of m. vastus lateralis during test has characteristic peak corresponding to AAT. The statistically significant correlation (r = 0.78, p < 0.05) between the load corresponding to AAT and anaerobic threshold (blood [La] = 4 mmol) was found during bicycle test. The method is applicable to determination of AAT during exercise of small muscle group.

Alterations in Whole-Body Insulin Sensitivity Resulting From Repeated Eccentric Exercise of a Single Muscle Group: A Pilot Investigation.

Unaccustomed eccentric exercise using large muscle groups elicits soreness, decrements in physical function and impairs markers of whole-body insulin sensitivity; although these effects are attenuated with a repeated exposure. Eccentric exercise of a small muscle group (elbow flexors) displays similar soreness and damage profiles in response to repeated exposure. However, it is unknown whether damage to small muscle groups impacts upon whole-body insulin sensitivity. This pilot investigation aimed to characterize whole-body insulin sensitivity in response to repeated bouts of eccentric exercise of the elbow flexors. Nine healthy males completed two bouts of eccentric exercise separated by 2 weeks. Insulin resistance (updated homeostasis model of insulin resistance, HOMA2-IR) and muscle damage profiles (soreness and physical function) were assessed before, and 48 h after exercise. Matsuda insulin sensitivity indices (ISI Matsuda) were also determined in 6 participants at the same time points as HOMA2-IR. Soreness was elevated, and physical function impaired, by both bouts of exercise (both p < .05) but to a lesser extent following bout 2 (time x bout interaction, p < .05). Eccentric exercise decreased ISI Matsuda after the first but not the second bout of eccentric exercise (time x bout interaction p < .05). Eccentric exercise performed with an isolated upper limb impairs whole-body insulin sensitivity after the first, but not the second, bout.

Low‐intensity training increases peak arm VO2 by enhancing both convective and diffusive O2 delivery

It is an ongoing discussion the extent to which oxygen delivery and oxygen extraction contribute to an increased muscle oxygen uptake during dynamic exercise. It has been proposed that local muscle factors including the capillary bed and mitochondrial oxidative capacity play a large role in prolonged low-intensity training of a small muscle group when the cardiac output capacity is not directly limiting. The purpose of this study was to investigate the relative roles of circulatory and muscle metabolic mechanisms by which prolonged low-intensity exercise training alters regional muscle VO2 . In nine healthy volunteers (seven males, two females), haemodynamic and metabolic responses to incremental arm cycling were measured by the Fick method and biopsy of the deltoid and triceps muscles before and after 42 days of skiing for 6 h day(-1) at 60% max heart rate. Peak pulmonary VO2 during arm crank was unchanged after training (2.38 ± 0.19 vs. 2.18 ± 0.2 L min(-1) pre-training) yet arm VO2 (1.04 ± 0.08 vs. 0.83 ± 0.1 L min(1) , P < 0.05) and power output (137 ± 9 vs. 114 ± 10 Watts) were increased along with a higher arm blood flow (7.9 ± 0.5 vs. 6.8 ± 0.6 L min(-1) , P < 0.05) and expanded muscle capillary volume (76 ± 7 vs. 62 ± 4 mL, P < 0.05). Muscle O2 diffusion capacity (16.2 ± 1 vs. 12.5 ± 0.9 mL min(-1) mHg(-1) , P < 0.05) and O2 extraction (68 ± 1 vs. 62 ± 1%, P < 0.05) were enhanced at a similar mean capillary transit time (569 ± 43 vs. 564 ± 31 ms) and P50 (35.8 ± 0.7 vs. 35 ± 0.8), whereas mitochondrial O2 flux capacity was unchanged (147 ± 6 mL kg min(-1) vs. 146 ± 8 mL kg min(-1) ). The mechanisms underlying the increase in peak arm VO2 with prolonged low-intensity training in previously untrained subjects are an increased convective O2 delivery specifically to the muscles of the arm combined with a larger capillary-muscle surface area that enhance diffusional O2 conductance, with no apparent role of mitochondrial respiratory capacity.