Correction to: Physiological resolution of periodic breath holding during heavy-intensity Fartlek exercise.

The original version of this article unfortunately contained a mistake.

Physiological resolution of periodic breath holding during heavy-intensity Fartlek exercise.

PURPOSE: The purpose was to compare the singular and combined effects of 5 s breath holds (BH) and 5 s sprints, every 30 s, during continuous high-intensity exercise, on ventilation ([Formula: see text]), oxygen uptake ([Formula: see text]O2) and associated kinetics (τ), carbon dioxide production ([Formula: see text]CO2), and arterialized-capillary lactate concentration ([La-]). METHODS: Ten men (24 ± 3 years) performed 4-6 min ergometer protocols that included a step-transition from 20 W to a power output of 50% of the difference between lactate threshold and [Formula: see text]O2 peak (Δ50%) including: (1) a continuous protocol (CONT) with free breathing, (2) an intermittent BH protocol (CONT-BH); repeated cycles of 5 s BH: 25 s free breathing, (3) a Fartlek protocol (Fartlek); repeated 5 s at peak aerobic power output: 25 s at Δ50%; (4) combining the 5 s Fartlek and CONT-BH protocol (Fartlek-BH). Breath-by-breath gas exchange, measured by mass spectrometry and turbine, was recorded. RESULTS: [Formula: see text] E (L min-1) was greater (p < 0.05) than CONT (90 ± 7) in all conditions CONT-BH (98 ± 16), Fartlek (105 ± 10), and Fartlek-BH (101 ± 19). [Formula: see text]O2 and [Formula: see text]CO2 (L min-1) were unchanged in CONT-BH (2.73 ± 0.14 and 3.16 ± 0.38) and greater in Fartlek (2.85 ± 0.12 and 3.43 ± 0.16), compared to CONT (2.71 ± 0.12 and 3.12 ± 0.13). Whereas, [Formula: see text]CO2 during Fartlek-BH was higher (3.28 ± 0.35) and [Formula: see text]O2 was unchanged (2.73 ± 0.14). Fartlek-BH resulted in slower [Formula: see text]O2 kinetics (62.2 ± 19 s) and greater blood lactate concentrations (11.5 ± 2.7 mM), compared to CONT (48.8 ± 12 s; 9.0 ± 2.3 mM, respectively). CONCLUSIONS: It was demonstrated that the CONT-BH resulted in increased ventilation that sustained [Formula: see text]O2. However, [Formula: see text]O2 was restricted when an additional work was combined with the BH condition.

The influence on sarcopenia of muscle quality and quantity derived from magnetic resonance imaging and neuromuscular properties.

The relative contributions of intrinsic and extrinsic neuromuscular factors on sarcopenia are poorly understood. The associations among age-related declines of strength, muscle mass, and muscle quality in response to motor unit (MU) loss have not been systematically investigated in the same groups of subjects. The purpose was to assess MU loss, MRI-derived muscle cross-sectional area (CSA), muscle protein quantity (MPQ), and normalized strength of the dorsiflexors in one group of young (~25 years) adult males compared with two groups of healthy men aged 60­85 years. Muscle strength was assessed on a dynamometer and was ~25 % lower in both older groups, but CSA was less only in the older (>75 years) men, with no differences between the young and old (60­73 years). Normalized strength tended to be lower in both groups of aged men compared to young. For MPQ, only the older men showed ~8 % lower values than the young and old men. Older men had fewer functioning MUs than old, and both groups of aged men had fewer MUs than young men. Muscle quality appears to be maintained in the old likely due to compensatory MU remodeling, but in the older group (>75 years), MU loss was higher and MPQ was lower.

Differential Age-related Changes in Bone Geometry between the Humerus and the Femur in Healthy Men.

Muscle pull and weight-bearing are key mechanical determinants of bone geometry which is an important feature of bone strength that declines with adult aging. However, the relative importance of these determinants in young and old adults has not been evaluated systematically. To differentiate the influence of each type of mechanical loading we compared humeral and femoral bone shaft geometry and cross-sectional area (CSA) of the arm and thigh muscles in young and old men. Contiguous transverse MRI (Siemens 1.5T) scans of the arm and thigh were made in 10 young men (21.9 ± 1.0 years) and 10 old men (78.1 ± 4.9 years). Image analysis yielded total (TA), cortical (CA) and medullary (MA) CSA of the humeral and femoral shafts, as well as muscle CSA of the corresponding regions of the arm and thigh. Humeral CA was significantly greater in the young, whereas humeral and femoral MA were significantly greater in the older group. Significant correlations were found between arm muscle CSA and humeral CA (r = 0.73); between thigh muscle CSA and femoral CA (r = 0.69); and between body mass and femoral CA (r = 0.63) and TA (r = 0.55). Moderate correlations between muscle CSA and CA suggest that muscle pull is an important determinant of bone geometry. The significant difference observed between young and old in humeral, but not femoral CA, and the correlation between body mass and femoral, but not humeral cortical area, suggests that weight-bearing attenuates bone loss associated with adult aging.

Differences in leg bone geometry in young, old and very old women.

Bone geometry is an important measure of bone strength and is known to be affected by weight-bearing and adult ageing. Engagement in weight-bearing activity decreases with age, thus in this study we compared bone geometry changes between weight-bearing (tibia) and non-weight-bearing (fibula) leg bones in three different age groups of women. Magnetic resonance images of the right leg were acquired in 9 young (20-27 years), 7 old (61-69 years) and 7 very old (71-80 years) women. Total and cortical bone volumes and medullary cavity volumes (mm(3)) were calculated at proximal and distal sites for both bones. Tibial cortical bone volume was significantly less at the proximal site in old (17%) and very old (24%) groups versus young subjects. Cortical bone volume in the proximal fibula was also significantly reduced in the older groups (7 and 12%), but to a substantially lesser extent than in the tibia. In contrast, distal bone geometry appeared largely to be conserved in both tibia and fibula. Proximally, medullary cavity volume was greater in the older groups in the tibia but not the fibula. Distally, the only difference found in either bone was a significantly greater fibular medullary cavity in the very old group. These findings suggest weight-bearing bones in women are more susceptible than non-weight-bearing bones to age-related changes in bone geometry likely due to decreases in weight-bearing activities. Also, weight-bearing activity appears to provide a greater osteogenic stimulus at the distal portions of the leg bones.

Effects of ammonium chloride ingestion on phosphocreatine metabolism during moderate- and heavy-intensity plantar-flexion exercise.

This study examined the effects of NH(4)Cl ingestion on phosphocreatine (PCr) metabolism during 9 min of moderate- (MOD) and heavy- (HVY) intensity constant-load isotonic plantar-flexion exercise. Healthy young adult male subjects (n = 8) completed both a control (CON) and NH(4)Cl ingestion (ACID) trial. Phosphorus-31 magnetic resonance spectroscopy was used to monitor changes in intracellular pH (pHi), [Pi], [PCr], and [ATP]. During the Middle (3-6 min) and Late (6-9 min) stages of HVY, ACID was associated with a higher (P < 0.05) intracellular hydrogen-ion concentration ([H(+)]i) [Middle: 246 (SD 36) vs. 202 (SD 36) mmol/l]; [Late: 236 (SD 35) vs. 200 (SD 39) mmol/l]. In addition, ACID was associated with a lower (P < 0.05) [PCr] relative to CON during the Early (0-3 min) [18.1 (SD 5.1) vs. 20.4 (SD 5.4) mmol/l] and Middle stages [14.1 (SD 5.4) vs. 16.7 (SD 6.0) mmol/l] of HVY. The amplitude of the primary component of PCr breakdown during the transition to HVY was greater in ACID than CON [14.5 (SD 5.8 vs. 11.3 (SD 4.8) mmol/l], however, the PCr slow component (continued slow decline in [PCr]) showed no difference (P > 0.05). The time constant for PCr breakdown (tauPCr) was greater in HVY than MOD for both conditions [58 (SD 22) vs. 28 (SD 15) s ACID; 51 (SD 20) vs. 29 (SD 14) s CON] (P < 0.05). In summary, ACID increased PCr breakdown during the transition from MOD to HVY, but did not increase the magnitude of the PCr slow component.

Geometry of a weight-bearing and non-weight-bearing bone in the legs of young, old, and very old men.

Bone geometry is an important determinant of bone strength and is influenced by muscle pull and weight-bearing. Muscle mass and exposure to weight-bearing decrease with age and thus the purpose of the study was to compare bone geometry of the weight-bearing (tibia) and non-weight-bearing (fibula) bones of the leg in different age groups. Magnetic resonance images of the right leg were acquired in 13 young (26 yr), 13 old (66 yr), and 13 very old men (83 yr). Cortical, medullary and total cross-sectional areas (CSA) of the bones were measured at approximately one-third and two-thirds the length of the leg. Muscle CSA of the anterior, lateral and posterior compartments was measured at the proximal site. Cortical CSA was approximately 14 to 22% smaller in the elderly in the tibia but similar across age in the fibula. Medullary CSA was larger with age (approximately 5 to 65%) in both bones but approximately 15 to 440% greater in the tibia than fibula. Total CSA was similar across age in both bones. Muscle mass was similar between young and old but approximately 25% less in the very old and as a consequence, the magnitude of differences in bone geometry at proximal and distal sites varied in the two elderly groups. These findings indicate that there is a complex age-dependent interaction between muscle pull and weight-bearing. The greater age-related differences in bone geometry in the tibia suggest the weight-bearing role of the tibia makes it more susceptible than the fibula to the reduced activity typically associated with aging.

Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with 31P-MRS.

In this study, we examined muscle metabolic and acid-base status during incremental wrist extension exercise in the forearm of individuals with work-related myalgia (WRM). Eighteen women employed in full-time occupations involving repetitive forearm labor were recruited in this cross-sectional study. Nine of these women were diagnosed with WRM, while the other nine had no previous WRM history and were used as age-matched controls (Con). Phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([P(i)]) as well as intracellular pH (pH(i)) status during exercise in WRM and Con. We observed a 38% decreased work capacity in WRM compared with Con [0.18 W (SD 0.03) vs. 0.28 W (SD 0.10); P = 0.007]. Piecewise linear regression of the incremental exercise data revealed that the onset of a faster decrease in pH(i) (i.e., the pH threshold, pHT) and the onset of a faster increase in log([P(i)]/[PCr]) (i.e., the phosphorylation threshold, PT) occurred at a 14% relatively lower power output in WRM [pHT: 45.2% (SD 5.3) vs. 59.0% (SD 4.6), P < 0.001; PT: 44.8% (SD 4.3) vs. 57.8% (SD 3.1), P < 0.001; % of peak power output, Con vs. WRM, respectively]. Monoexponential modeling of the kinetics of [PCr] and pH(i) recovery following exercise demonstrated a slower (P = 0.005) time constant (tau) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower (P = 0.007) tau for pH(i) in WRM [370 s (SD 178)] vs. Con [179 s (SD 52)]. In conclusion, our results suggest that WRM is associated with an increased reliance on nonoxidative metabolism. Possible mechanisms include a reduction in local muscle blood flow and perfusion, an increased ATP cost of force production, or both.

Prior exercise delays the onset of acidosis during incremental exercise.

The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (approximately 0.6 W/min) to volitional fatigue (Ramp); 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT; Mod-Ramp); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT (Hvy-Ramp); the constant-load and incremental exercise periods were separated by 6 min of rest. (31)P-magnetic resonance spectroscopy was used to continuously monitor intracellular pH, phosphocreatine concentration ([PCr]), and inorganic phosphate concentration ([P(i)]). No differences in exercise performance or the metabolic response to exercise were observed between Ramp and Mod-Ramp. However, compared with Ramp, a 14% (SD 10) increase (P < 0.01) in peak power output (PPO) was observed in Hvy-Ramp. The improved exercise performance in Hvy-Ramp was accompanied by a delayed (P = 0.01) onset of intracellular acidosis [Hvy-Ramp 60.4% PPO (SD 11.7) vs. Ramp 45.8% PPO (SD 9.4)] and a delayed (P < 0.01) onset of rapid increases in [P(i)]/[PCr] [Hvy-Ramp 61.5% PPO (SD 12.0) vs. Ramp 45.1% PPO (SD 9.1)]. In conclusion, prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.

Characteristics of a MR-compatible ankle exercise ergometer for a 3.0 T head-only MR scanner.

An exercise ergometer, for isometric or dynamic contraction of both dorsiflexion and/or plantarflexion exercise, was designed and constructed for a 3.0 T head-only MR scanner. The principal features of this MR-compatible ergometer include electronic devices for quantification of force (during isometric exercise) and angular displacement (during dynamic exercise), without any significant losses to external motions or frictions. The ergometer was also made to be adjustable for subject leg length and was designed for suspension within the bore of the magnet to eliminate transmission of force and vibration to the MR scanner. A description of the design and construction, as well as the important technical features, is presented herein.

Effects of maximal isometric and isokinetic resistance training on strength and functional mobility in older adults.

BACKGROUND: The aim of the present study was to compare the changes in voluntary strength (isometric, concentric, and eccentric) and functional mobility in response to maximal isokinetic eccentric-only resistance training to those elicited by maximal isometric-only or maximal isokinetic concentric-only resistance training in older adults. METHODS: Twelve women (73 +/- 7 years) and 18 men (73 +/- 5 years) completed a 12-week training program (three times per week) using a Biodex System 3 dynamometer. Primary outcome measures included peak isometric and isokinetic (concentric and eccentric) knee extensor strength, concentric work, concentric power, stair ascent and descent, and gait speed. Participants were randomly assigned to one of three training groups: isometric-only, isokinetic concentric-only, or isokinetic eccentric-only. RESULTS: All three training groups demonstrated an increase in peak isometric and isokinetic concentric and eccentric strength following 12 weeks of training (p <.01). Step time was positively influenced (p <.03) by all three training modes; however, gait speed was unchanged following 12 weeks of training. All three training groups experienced a significant increase in peak concentric work and concentric power (p <.01) with the concentric training group demonstrating the largest increases in both peak concentric work and concentric power when compared to the isometric and eccentric training groups. CONCLUSIONS: It was clear that all three resistance training programs (isometric, concentric, and eccentric) in older adults were effective in increasing strength, concentric work, and concentric power over the 12-week training period. Furthermore, 12 weeks of resistance training resulted in improved stair ascent and descent performance.

Reliability of a single-session isokinetic and isometric strength measurement protocol in older men.

BACKGROUND: The purposes of the current study were (a) to determine the test-retest reliability of a single-session isokinetic and isometric strength testing protocol in older healthy men, and (b) to compare the outcomes of the reliability measures derived from averaged torque scores with those derived from a single peak torque score. METHODS: In 19 men (mean age, 72 +/- 5 years), both lower limbs were assessed independently on 2 separate test days using the Biodex System 3 dynamometer. After completing a 5-minute warm-up, each man performed three submaximal knee extensions followed by five maximal contractions at 90 degrees /s (CON), 0 degrees /s (ISO), and -90 degrees /s (ECC). Average (best 3 of 5) and peak CON, ISO, and ECC torque, and CON work and CON power were determined. Peak CON work and CON power were recorded from the highest peak torque concentric contraction (HPTCC). RESULTS: Intraclass correlation coefficients ranging from 0.84 to 0.94 were found to have good reliability. The typical error as a coefficient of variation ranged from 8% to 10% for averaged measures and from 8% to 17% for peak torque and HPTCC. The ratio limits of agreement for average and peak CON, ISO, and ECC torque ranged from 23% to 33% and from 40% to 54% for average CON and HPTCC work and power. CONCLUSIONS: The test-retest reliability of a single-session isokinetic and isometric strength testing protocol in this group of older healthy men displayed good relative reliability (intraclass correlation coefficient > 0.84); however, because the typical error as a coefficient of variation and ratio limits of agreement (absolute reliability) were large, single-session testing is not recommended.

Metabolic effects of induced alkalosis during progressive forearm exercise to fatigue.

Metabolic alkalosis induced by sodium bicarbonate (NaHCO(3)) ingestion has been shown to enhance performance during brief high-intensity exercise. The mechanisms associated with this increase in performance may include increased muscle phosphocreatine (PCr) breakdown, muscle glycogen utilization, and plasma lactate (Lac(-)(pl)) accumulation. Together, these changes would imply a shift toward a greater contribution of anaerobic energy production, but this statement has been subject to debate. In the present study, subjects (n = 6) performed a progressive wrist flexion exercise to volitional fatigue (0.5 Hz, 14-21 min) in a control condition (Con) and after an oral dose of NaHCO(3) (Alk: 0.3 g/kg; 1.5 h before testing) to evaluate muscle metabolism over a complete range of exercise intensities. Phosphorus-31 magnetic resonance spectroscopy was used to continuously monitor intracellular pH, [PCr], [P(i)], and [ATP] (brackets denote concentration). Blood samples drawn from a deep arm vein were analyzed with a blood gas-electrolyte analyzer to measure plasma pH, Pco(2), and [Lac(-)](pl), and plasma [HCO(3)(-)] was calculated from pH and Pco(2). NaHCO(3) ingestion resulted in an increased (P < 0.05) plasma pH and [HCO(3)(-)] throughout rest and exercise. Time to fatigue and peak power output were increased (P < 0.05) by approximately 12% in Alk. During exercise, a delayed (P < 0.05) onset of intracellular acidosis (1.17 +/- 0.26 vs. 1.28 +/- 0.22 W, Con vs. Alk) and a delayed (P < 0.05) onset of rapid increases in the [P(i)]-to-[PCr] ratio (1.21 +/- 0.30 vs. 1.30 +/- 0.30 W) were observed in Alk. No differences in total [H(+)], [P(i)], or [Lac(-)](pl) accumulation were detected. In conclusion, NaHCO(3) ingestion was shown to increase plasma pH at rest, which resulted in a delayed onset of intracellular acidification during incremental exercise. Conversely, NaHCO(3) was not associated with increased [Lac(-)](pl) accumulation or PCr breakdown.

Reliability of isokinetic and isometric knee-extensor force in older women.

Because of the need for efficient, consistent strength measurements, the test-retest reliability of concentric, isometric, and eccentric strength; concentric work; and concentric power was determined in older women without a familiarization session. The reliability of measures derived from a single peak score were compared with those derived from an averaged score. On 2 occasions 25 older women with a mean age of 72 +/- 6 years performed 3 submaximal knee extensions and 5 maximal contractions on an isokinetic dynamometer at 90 degrees/s (CON), 0 degrees/s, and -90 degrees/s on both lower limbs. Statistical analyses for peak and averaged values (best 3 contractions of 5) exhibited good relative reliability (ICCs > .88), except for CON power. Typical error as a coefficient of variation and ratio limits of agreement for peak and averaged score values were larger than desired, with CON power scores demonstrating unacceptable error ranges. Although relative reliability of this 1-session assessment protocol was acceptable, further research is needed to determine whether additional practice trials could enhance absolute reliability.

Muscle fiber number in the biceps brachii muscle of young and old men.

We have compared the number of muscle fibers in the biceps brachii muscle (BB) of six old men (82.3 +/- 4.3 years) and six young men (21.2 +/- 1.9 years). Muscle fiber number was estimated by dividing the maximal area of the BB, determined with magnetic resonance imaging, by the mean fiber area of the BB determined in a muscle biopsy. The percentage of type II fibers in the BB ( approximately 60%) and the type I fiber area were not different between the groups. The BB area (-26%), type II fiber area (-24%), mean fiber area (-20%), and maximal voluntary contraction strength (MVC) of the elbow flexor muscles (-27%) were lower in the old than young group. However, the estimated number of muscle fibers was not significantly different between the young (253000) and old (234000) men. Consequently, the smaller BB area of the old men could be explained primarily by a smaller type II fiber size. These findings suggest that old age is not associated with a reduced number of muscle fibers in the BB. The relative contribution of a reduction in fiber number to age-related muscle atrophy may be muscle-dependent.

Changes in human muscle transverse relaxation following short-term creatine supplementation.

The rapid increase in body mass that often occurs following creatine (Cr) supplementation is believed to be due to intracellular water retention. The purpose of this study was to determine whether Cr consumption alters the magnetic resonance (MR) transverse relaxation (T(2)) distribution of skeletal muscle. Transverse relaxation can be used to model water compartments within a cell or tissue. In this double-blind study, subjects were asked to supplement their normal diet with creatine monohydrate (20 g day(-1) for 5 days) mixed with a grape drink (Creatine group, n = 7), or the grape drink alone (Placebo group, n = 8). Phosphorous MR spectroscopy was used to determine the effectiveness of the supplementation protocol. Subjects that responded to the Cr supplementation (i.e. showed a > 5 % increase in the ratio of the levels of phosphocreatine (PCr) and ATP) were placed in the Creatine group. Both proton MR imaging and spectroscopy were used to acquire T(2) data, at 1.89 T, from the flexor digitorum profundus muscle of each subject before and after supplementation. Following the supplementation period, the Creatine group showed a gain in body mass (1.2 +/- 0.8 kg, P < 0.05, mean +/- S.D.), and an increase in PCr/ATP ratio (23.8 +/- 16.4 %, P < 0.001). Neither group showed any changes in intracellular pH or T(2) calculated from MR images. However, the spectroscopy data revealed at least three components (> 5 ms) at approximately 20, 40 and 125 ms in both groups. Only in the Creatine group was there an increase in the apparent proton concentration of the two shorter components combined (+5.0 +/- 4.7 %, P < 0.05). According to the cellular water compartment model, the changes observed in the shorter T(2) components are consistent with an increase in intracellular water.