Semi-reclined Position Research Articles

No Mitochondrial Related Transcriptional Changes in Human Skeletal Muscle after Local Heat Application.

The purpose of the study is to determine the impact of local heating on skeletal muscle transcriptional response related to mitochondrial biogenesis and mitophagy. Twelve healthy subjects (height, 176.0 ± 11.9 cm; weight, 83.6 ± 18.3 kg; and body composition, 19.0 ± 7.7% body fat) rested in a semi-reclined position for 4 h with a heated thermal wrap (HOT) around one thigh and a wrap without temperature regulation (CON) around the other (randomized). Skin temperature, blood flow, intramuscular temperature, and a skeletal muscle biopsy from the vastus lateralis were obtained after the 4 h intervention. Skin temperature via infrared thermometer and thermal camera was higher after HOT (37.3 ± 0.7 and 36.7 ± 1.0 °C, respectively) than CON (34.8 ± 0.7, 35.2 ± 0.8 °C, respectively, p < 0.001). Intramuscular temperature was higher in HOT (36.3 ± 0.4 °C) than CON (35.2 ± 0.8 °C, p < 0.001). Femoral artery blood flow was higher in HOT (304.5 ± 12.5 mL‧min-1) than CON (272.3 ± 14.3 mL‧min-1, p = 0.003). Mean femoral shear rate was higher in HOT (455.8 ± 25.1 s-1) than CON (405.2 ± 15.8 s-1, p = 0.019). However, there were no differences in any of the investigated genes related to mitochondrial biogenesis (PGC-1α, NRF1, GAPBA, ERRα, TFAM, VEGF) or mitophagy (PINK-1, PARK-2, BNIP-3, BNIP-3L) in response to heat (p > 0.05). These data indicate that heat application alone does not impact the transcriptional response related to mitochondrial homeostasis, suggesting that other factors, in combination with skeletal muscle temperature, are involved with previous observations of altered exercise induced gene expression with heat.

Cervical Spine Musculotendon Lengths When Reading a Tablet in Three Seated Positions.

A popular posture for using wireless technology is reclined sitting, with the trunk rotated posteriorly to the hips. This position decreases the head's gravitational moment; however, the head angle relative to the trunk is similar to that of upright sitting when using a tablet in the lap. This study compared cervical extensor musculotendon length changes from neutral among 3 common sitting postures and maximum neck flexion while using a tablet. Twenty-one participants had radiographs taken in neutral, full-flexion, and upright, semireclined, and reclined postures with a tablet in their lap. A biomechanical model was used to calculate subject-specific normalized musculotendon lengths for 27 cervical musculotendon segments. The lower cervical spine was more flexed during reclined sitting, but the skull was more flexed during upright sitting. Normalized musculotendon length increased in the reclined compared with an upright sitting position for the C4-C6/7 (deep) and C2-C6/7 (superficial) multifidi, semispinalis cervicis (C2-C7), and splenius capitis (Skull-C7). The suboccipital (R2 = .19-.71) and semispinalis capitis segment length changes were significantly correlated with the Skull-C1 angle (0.24-0.51). A semireclined reading position may be an ideal sitting posture to reduce the head's gravitational moment arm without overstretching the assessed muscles.

Long Term Habituation To Carbohydrate-Restricted Diet Preserved Performance And Central Drive After 2 Hours Of Running: A Case Study

PURPOSE: While the brain is usually wholly dependent on glucose for fuel, prolonged carbohydrate deprivation results in adaptations that allow the brain to access fat via ketone bodies. Given the depletion of carbohydrate that takes place during prolonged exercise, a shift toward ketone bodies may maintain central nervous system function, preventing the central fatigue observed during long-duration exercise. In addition, enhancing peripheral muscle’s use of free fatty acids and intra-muscular lipids might prolong contractions. Thus, high fat/low carb diets have been proposed to delay fatigue during endurance exercise. However, studies utilizing periods of 1 to 5 weeks of adaptation to high fat diets have shown equivocal changes in performance at moderate or high intensities. We compare endurance and time trial performance of a keto-adapted male runner (KETO) to 8 subjects (NORM) on whom we have previously reported. METHODS: We measured peripheral and central fatigue in 8 men runners (38±2 yrs; VO2peak 59±3 ml/kg/min) who habitually ate a carbohydrate-liberal diet (NORM) and in a runner (41 yrs, 70 ml/kg/min) who followed a high fat/low carb diet for >2 years. Water was provided at 1% of body mass/hr, during a 2-hr run at ventilatory threshold (~65% VO2peak), followed by a self-paced 2-km time trial (TT). RPE and respiratory measures were determined every 20 minutes. Strength was tested in a semi-reclined position [75° hip flexion, to facilitate femoral nerve stimulation] pre-exercise, after the 2-hr run and post-time trial as follows: voluntary isometric quad strength was measured on the Biodex with the knee flexed 60°, and with superimposed peripheral magnetic stimulation of the femoral nerve to determine central activation (CAR). RESULTS: Respiratory exchange ratio indicated that KETO (0.78) used less carbohydrate than NORM (0.86±0.01) during the 2-hr run. While we measured no fatigue of any kind in KETO, NORM declined in voluntary strength (-16±5%) and experienced loss of central drive to the muscle (CAR decreased from 0.85±0.04 to 0.76±0.05). KETO ran the TT at a mean pace of 16.4 km/hr compared to 14.8±0.7 km/hr in NORM. CONCLUSIONS: Our KETO runner did not display strength loss and may have had better TT performance after exhausting exercise as compared to our NORM runners who exhibited central fatigue.

Enhancement of knee extension voluntary and electrically-evoked strength with the body tilted backward

BACKGROUND: While extreme changes in body position (e.g., standing vs. sitting) have been shown to affect knee extensor strength, little is known regarding how less extreme changes in body position affect knee extensor strength and activation. OBJECTIVE: This study evaluated the effect of four seat ed positions on the maximum voluntary isometric contraction (MVIC) and electrically-evoked isometric strengths of the knee extensors. METHODS: Forty healthy subjects participated. MVIC strength, electrically-evoked strength, and voluntary activation of the quadriceps muscles were measured under four seated positions: 1) 22.5–25∘ forward tilt, 2) 0∘ tilt, 3) 22.5–25∘ backward tilt, and 4) 45–50∘ backward tilt. The effect of seated position on each dependent variable was assessed using a one-way repeated measures ANOVA with linear contrasts. RESULTS: MVIC and electrically-evoked strengths increased (P⩽ 0.037) by 5–11% as the body was moved from the 22.5–25∘ forward-tilted to 45–50∘ backward-tilted position. However, voluntary muscle activation and EMG amplitudes of the knee extensors during MVIC did not change. CONCLUSIONS: Knee extensor MVIC and electrically-evoked strengths were modestly enhanced as the body was tilted backwards. The use of a semi-reclined position may assist in obtaining a more forceful contraction of the knee extensors, thereby potentially resulting in better strength training outcomes.

Patterns of lower limb muscular activity and joint moments during directional efforts using a static dynamometer

BackgroundStrength and coordination of lower muscle groups typically identified in healthy subjects are two prerequisites to performing functional activities. These physical qualities can be impaired following a neurological insult. A static dynamometer apparatus that measures lower limb joint moments during directional efforts at the foot was developed to recruit different patterns of muscular activity. The objectives of the present study were to 1) validate joint moments estimated by the apparatus, and 2) to characterize lower limb joint moments and muscular activity patterns of healthy subjects during progressive static efforts. Subjects were seated in a semi-reclined position with one foot attached to a force platform interfaced with a laboratory computer. Forces and moments exerted under the foot were computed using inverse dynamics, allowing for the estimation of lower limb joint moments.To achieve the study’s first objective, joint moments were validated by comparing moments of various magnitudes of force applied by turnbuckles on an instrumented leg equipped with strain gauges with those estimated by the apparatus. Concurrent validity and agreement were assessed using Pearson correlation coefficients and Bland and Altman analysis, respectively. For the second objective, joint moments and muscular activity were characterized for five healthy subjects while exerting progressive effort in eight sagittal directions. Lower limb joint moments were estimated during directional efforts using inverse dynamics. Muscular activity of eight muscles of the lower limb was recorded using surface electrodes and further analyzed using normalized root mean square data.ResultsThe joint moments estimated with the instrumented leg were correlated (r > 0.999) with those measured by the dynamometer. Limits of agreement ranged between 8.5 and 19.2% of the average joint moment calculated by both devices. During progressive efforts on the apparatus, joint moments and patterns of muscular activity were specific to the direction of effort. Patterns of muscular activity in four directions were similar to activation patterns reported in the literature for specific portions of gait cycle.ConclusionThis apparatus provides valid joint moments exerted at the lower limbs. It is suggested that this methodology be used to recruit muscular activity patterns impaired in neurological populations.

Prevalence of breastfeeding in a baby-friendly pediatric practice: an experience in Trieste, Italy

BackgroundIn a pediatric practice in Italy, actions were undertaken to apply the recommendations for a breastfeeding-friendly physician’s office and to promote the adoption of a semi-reclined or laid-back maternal position in breastfeeding. The aim of this study is to evaluate the effect of the actions implemented, in terms of prevalence of exclusive breastfeeding.MethodsA historical cohort study was carried out using administrative data routinely collected. All women who gave birth in 2016 and registered their newborns with the pediatric practice were included, only mothers of preterm newborns < 30 weeks gestational age were excluded. The main actions undertaken were: employment of a breastfeeding peer supporter; ensuring unlimited daily access in case of breastfeeding difficulties; provision of individual support to breastfeeding mothers in a dedicated room and advice on the laid-back position; scheduling of weekly meetings of small groups for breastfeeding support. Each infant was followed up for five months. The main study outcomes were duration of exclusive breastfeeding (only breast milk and no other liquids or solids, except for drops of syrups with nutritional supplements or medicines) and prevalence at five months.ResultsA total of 265 newborn infants with a gestational age greater than 30 weeks were registered with the pediatric practice during the study period, about 18% of all infants born in Trieste in that period. Complete data were available for 252 of these (95.1%). The rate of exclusive breastfeeding at five months of age was higher than the one reported for the whole infant population of Trieste and of the Friuli Venezia Giulia Region (62.3% vs. 42.9% vs. 30.3%) in the same period.ConclusionsThe implementation of breastfeeding-friendly pediatric practice and the application of laid-back breastfeeding may improve the rate and duration of exclusive breastfeeding.

To Test or Not to Test: A Retrospective Review of Infant Car Seat Tolerance Screening at a Single Institution

OBJECTIVES: The American Academy of Pediatrics (AAP) recommends all neonates born at <37 weeks gestational age (GA), and all infants at risk for cardiorespiratory compromise while seated in a semi-reclined position, undergo Car Seat Tolerance Screening (CSTS) prior to discharge. This test requires significant staff time and resources to complete, and there is tremendous variation in not only criteria and methodology for testing, but also for what constitutes passage or failure. To inform best-practice recommendations, we examined CSTS outcomes among infants tested over a 33-month period at a …

Similar Central and Peripheral Fatigue in Men and Women after Running

PURPOSE: Women may be less fatiguable than men during prolonged endurance exercise. There are a paucity of studies which have compared fatigue in both sexes after moderately long duration running typical of marathon-type training. METHODS: We compared sex differences in peripheral and central fatigue in 8 men and 6 premenopausal women runners. Volunteers [38±2 and 32±2 yrs, p=0.017; VO2peak 59±3 and 54±3, ml/kg/min, p=0.202, men vs women respectively] ate a standardized breakfast [6 Kcal/kg] 90 minutes prior to commencing testing. Water was provided at 1% of body mass/hr, during a 2-hr run at their ventilatory threshold [~65% VO2peak], followed by a self-paced 2-km time trial. RPE and respiratory measures were determined every 20 minutes. Strength was tested in a semi-reclined position [75o hip flexion, to facilitate femoral nerve stimulation] pre-exercise, after the 2-hr run and post-time trial as follows: voluntary isometric quad strength was measured on the Biodex with the knee flexed 60°, and with superimposed peripheral magnetic stimulation [PMS] of the femoral nerve to determine central activation [CAR]. PMS was also applied in a 3-second pulse train on a relaxed muscle to measure peripheral fatigue. Changes in strength and in metabolic measures were analyzed with repeated measures ANOVA. RESULTS: Following running, voluntary strength declined by ~16% in both sexes [effect of time p<0.001; sex X time p=0.206]. CAR also decreased in both men and women [effect of time p=0.020, time X sex p=0.762]. PMS-stimulated forces, our measure of peripheral fatigue, were unchanged after running: there was no effect of time [p=0.10] in men or women [time X sex, p=0.322]. Substrate use and RPEs did not differ between sexes. CONCLUSIONS: We found that both sexes fatigued similarly after a 2-hr run plus a 2-km time trial, and that all of the fatigue was central in nature. While women may be more fatigue-resistant than men, those differences might not be apparent until a greater duration of running is engaged in, e.g. ultramarathon distances.

Low pressure hydrocephalus: clinical manifestations, radiological characteristics, and treatment

Low pressure hydrocephalus (LPH) is a rare type of hydrocephalus with low intracranial pressure and ventriculomegaly. The recognition of LPH is important, and the treatment is difficult and very complicated. An understanding of how to drain cerebrospinal fluid when the intracranial pressure is lower than the opening pressure of the value represents a critical issue. Seven patients who suffered from the pain of hydrocephalus syndrome and were diagnosed with LPH were retrospectively reviewed. A ventricle peritoneal shunt was applied to all patients, and the valve system was adjusted to the lowest pressure; however, the clinical manifestations of hydrocephalus in five of seven patients did not improve over one week. Intermittent pressing of the valve in combination with the maintenance of a semi-reclined position were subsequently implemented. The symptoms of hydrocephalus began to improve from three days to two months following the initiation of intermittent valve pressing in combination with the maintenance of a semi-reclined position. At the twelve months follow up, six of seven patients (85.7%) showed good recovery to minimal disability. Intermittent valve pressing in combination with a semi-reclined position is an effective and easy method to drain cerebrospinal fluid when the intracranial pressure (ICP) is lower than the opening pressure of the value and improve hydrocephalus symptoms.

The influence of a semi-reclined seated posture on head and neck kinematics and muscle activity while reading a tablet computer

Increased tablet computer usage calls for a proper understanding of potential injury risks from these devices. The purpose of this study was to assess the influence of tablet computer reading postures on head and neck flexion and muscle activity. Nineteen participants completed read a tablet computer in four different postures (standard computer monitor, tablet on a desk, tablet in the lap, semi-reclined with tablet in the lap). Reading the tablet in a semi-reclined trunk posture with the tablet in one's lap increased (p < 0.001) neck flexion angle (71.6%ROM) relative to reading from the standard computer monitor (6.39%ROM). Head flexion in the semi-reclined posture (19.7%ROM) and muscle activity (8.88%MVC) were similar to when reading from a standard computer monitor. Despite potentially reducing the gravitational moment produced by the head, the semi-reclined position could still compromise the force capabilities of the neck extensor musculature and result in increased strain on the passive tissues of the spine. Future work should assess how the semi-reclined position influences cervical intervertebral angles and passive tissue properties of the cervical spine. Overall, more research needs to be conducted on thoracic spine kinematics while reading a tablet computer.

Trunk Posture Influences Neck Angle When Reading A Tablet Computer

In 2013, 64% of American households owned a handheld computer device (e-reader, tablet, smartphones, etc.). The presence of these devices has grown more quickly than our understanding of their effects on musculoskeletal disorders. Their use on a tabletop or a person’s lap causes increased head and neck flexion, as well as an inreased gravitational moment produced by the weight of the head (Straker et al., 2009, Young et al., 2012, Vasavada et al., 2015). A limitation to these studies is that they keep a standard trunk position throughout all tasks; however, people can also assume a semi-reclined position when reading a tablet. The purpose of this study was to determine the influence of a semi-reclined trunk position on neck and head flexion angle, and cervical erector spinae muscle activity. Nineteen participants (10 male, 9 female) read off of a tablet in four postures: with the tablet in their lap, on a tabletop, off of a standard computer monitor, and semi-reclined to an angle of 30 degrees from the vertical. Having the tablet on the lap ( M=16%MVC, SD=8%MVC) significantly increased muscle activity of the cervical erector spinae ( p=.0023) compared to reading off of a monitor or in the semi-reclined position (approximately 10%MVC). Neck and head flexion angles significantly increased ( p&lt;.001) when reading the tablet off the lap (neck M=56.8o, SD=17.3o; head M=53.4o, SD=12.9o) versus the computer (neck M=6.4o, SD=6.4o; head M=8.2o, SD=7.4o), however, the head angle during semi-reclined reading stayed more vertical despite having the highest increase in neck flexion angle (neck M=71.6o, SD=14.0o; head M=19.7o, SD=9.2o). In the semi-reclined position, the gravitational moment of the head is second smallest for the four reading positions. In theory, this is desired as the moment that must be produced by the musculature and surround tissues would be less. The downside to this posture is that many of the neck extensor muscles may still not be in optimal force and moment production position. Many of the neck muscles that assist with extension originate from C5 to T5 and insert on C5 and above (Vasavada et al., 1998). At 30 degrees of neck flexion, the moment generating capability of the spenius and semispinalis muscles are decreased compared to when at a neutral position and fascicle length of splenius cervicis, capitis, and semispinalis capitis muscles experience changes of more than 70% of optimal length (Vasavada et al., 1998). While many of the extensor muscles only show moment arms that vary by 1 cm or less, for some there can be about a 2-3 cm changes as one goes from a flexed to extended neck posture (Vasavada et al., 1998). These combined changes mean that the force producing capabilities of the neck extensor muscles may be compromised a semi-reclined position. Future studies should report torso angle to properly analyze biomechanical risk factors during handheld computer use and compare results between studies.

Does the Mother’s Posture Have a Protective Role to Play During Skin-to-Skin Contact? Research Observations and Theories

Skin-to-skin contact during the first hour following birth is the gold standard in breastfeeding. Although consecutive meta-analyses report no adverse effects, a recent review shows an increase in idiopathic sudden unexpected postnatal collapse (SUPC) in healthy term babies identifying three main risk factors: skin-to-skin contact, breastfeeding, and baby lying prone. Concurrently, authoritative visual materials tacitly promote maternal supine postures illustrating the breast crawl, a form of birth skin-to-skin contact. The naked baby lies on top of his or her mother’s body, in close ventral contact with torso parallel to the floor—a position strongly associated with sudden infant death. Biological nurturing (BN) research, the first to examine maternal postural effects on breastfeeding success, suggests that a semireclined maternal position is optimal for breastfeeding initiation. The maternal body slope ensures that the baby lies tilted, a position known to promote oxygenation. The angle of maternal recline, a variable central to BN but hitherto ignored in the skin-to-skin and SUPC literature, is unrelated to dress level. This commentary develops a postural argument to increase understanding of the potential role played by the maternal body slope to reduce the risk of idiopathic SUPC.

Sex differences in central and peripheral mechanisms of fatigue in cyclists

We examined peripheral versus central contributions to fatigue in men and women during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. 11 men (41 ± 3 years) and 9 women (38 ± 2 years) cycled for 2 h at ventilatory threshold with 5, 1-min sprints interspersed, followed by a 3-km time trial. Quadriceps strength testing was performed isometrically in a semi-reclined position pre- and post-cycling: (1) MVC; (2) MVC with superimposed 3-s magnetic stimulation to measure central activation ratio (CAR), a measure of central fatigue; (3) peripheral magnetic stimulation (PMS) alone of the femoral nerve in a 4-s pulse train, a measure of peripheral fatigue. Data were analyzed with mixed model ANOVA. When adjusted for body mass, men and women had similar strength (p = 0.876), and changes in MVC with time were similar between sexes, declining 22 % in men and 16 % in women (p = 0.360). CAR was similar between sexes and decreased 15 % (effect of time, p < 0.001). Changes in PMS-elicited force were different between sexes: only men lost stimulated strength (6.30 to 5.21 vs. 5.48 to 5.53 N kg(-1), interaction p = 0.036). Results clearly demonstrate that quadriceps fatigue after >2 h of cycling was of both central and peripheral origin in men but solely due to central mechanisms in women.

Is there an advantage for preterm infants to feed orally in an upright or sidelying position?

Over the last decade, nursing staff and feeding therapists have promoted the upright and sidelying bottle feeding positions as ‘optimal’ for preterm infants. To verify such benefits, very low birth weight infants were randomized to being fed in the customary semi-reclined (control), upright, or sidelying position. The primary outcome was days from start to independent oral feeding. Secondary outcomes included infants' oral feeding skill levels monitored when taking 1,2, 3–5, and 6–8 oral feedings per day. Infants fed in the upright and sidelying groups attained independent oral feeding within the same number of days as control counterparts. There was no difference in the maturation of their oral feeding skills.

Influence of Cold Water Immersion on Limb and Cutaneous Blood Flow at Rest

Background: Cold water immersion reduces exercise-induced muscle damage. Benefits may partly arise from a decline in limb blood flow; however, no study has comprehensively investigated the influence of different degrees of cooling undertaken via cold water immersion on limb blood flow responses. Purpose: To determine the influence of cold (8°C) and cool (22°C) water immersion on lower limb and cutaneous blood flow. Study Design: Controlled laboratory study. Methods: Nine men were placed in a semireclined position and lowered into 8°C or 22°C water to the iliac crest for two 5-minute periods interspersed with 2 minutes of nonimmersion. Rectal and thigh skin temperature, deep and superficial muscle temperature, heart rate, mean arterial pressure, thigh cutaneous blood velocity (laser Doppler), and superficial femoral artery blood flow (duplex ultrasound) were measured during immersion and for 30 minutes after immersion. Indices of vascular conductance were calculated (flux and blood flow/mean arterial pressure). Results: Reductions in rectal temperature (8°C, 0.2° ± 0.1°C; 22°C, 0.1° ± 0.1°C) and thigh skin temperature (8°C, 6.2° ± 0.5°C; 22°C, 3.2° ± 0.2°C) were greater in 8°C water than in 22°C (P < .01). Femoral artery conductance was reduced to a similar extent immediately after immersion (~30%) and 30 minutes after immersion (~40%) under both conditions (P < .01). In contrast, there was less thigh cutaneous vasoconstriction during and after immersion in 8°C water compared with 22°C (P = .01). Conclusion: These data suggest that immersion at both temperatures resulted in similar whole limb blood flow but, paradoxically, more blood was distributed to the skin in the colder water. This suggests that colder temperatures may be associated with reduced muscle blood flow, which could provide an explanation for the benefits of cold water immersion in alleviating exercise-induced muscle damage in sports and athletic contexts. Clinical Relevance: Colder water temperatures may be more effective in the treatment of exercise-induced muscle damage and injury rehabilitation because of greater reductions in muscle blood flow.

Hypnotizability-related EEG alpha and theta activities during visual and somesthetic imageries

Hypnotizability is a cognitive multidimensional trait that involves peculiar imagery characteristics. Subjects with high- (Highs) and low (Lows)-susceptibilities to hypnosis have shown different levels of skill at visual and somesthetic-guided imageries performed during upright stance. The aim of this experiment is to study the modulation of the EEG alpha and theta band amplitude during guided visual and somesthetic imageries in Highs and Lows, as these rhythms are responsive to the cognitive activities involved in mental imagery. Our results show that, at variance with standing subjects, subjects in both groups in a semi-reclined position report higher vividness and lower effort for visual than for somesthetic imagery. EEG patterns however are different between the two groups. Highs exhibit a more widespread alpha desynchronization and slightly different EEG patterns during visual and somesthetic imageries, while Lows show segregated alpha- and theta-desynchronization, without any difference between the tasks. Our results indicate that different, hypnotizability-related cognitive strategies, that are revealed by differences in EEG modulation, are responsible for the similar subjective experience associated with visual and somesthetic imageries in Highs and Lows. In addition, in both groups higher order mental representation of different sensory modalities might be subserved by a unique integrated neural network.

Central Fatigue in Male and Female Cyclists Evaluated by Peripheral Magnetic Stimulation

It is well-known that men and women fatigue differently. However, the relative contributions of central vs. peripheral mechanisms to fatigue in men vs. women has not been examined. PURPOSE: To examine peripheral vs. central contributions to fatigue in men and women during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. METHODS: 11 men [41±3 yrs] and 6 women [39±4 yrs] cycled for 2 hours at approximately 66% of VO2peak[56±2 ml/Kg/min men, 53±4 women, P =0.419] with 5, 1-minute sprints interspersed, followed by a 3-Km time trial. Oxygen consumption was measured every 20 minutes to verify energy expenditure at the ventilatory threshold. Ratings of perceived exertion [RPE] were measured at the same time, as well as during each sprint using a Borg scale. Quadriceps isometric strength testing was performed in a semi-reclined position pre- and post-cycling: 1) MVC; 2) MVC with superimposed 3-second magnetic stimulation to measure central activation ratio [CAR]; 3) femoral nerve stimulation in a 4-second pulse train. Subjects recovered for 1 minute between contractions. Changes in metabolic and strength measurements over time and between gender were analyzed with repeated measures ANOVA. RESULTS: Heart rate [p=0.005] and RPE [p=0.013] increased over time during the 2 hours, with no differences between men and women. MVCs declined by 22% in men and 20% in women [effect of time, p90% MVC in men and >88% MVC in women. CONCLUSION: Results clearly demonstrate fatigue with a significant central component after prolonged cycling in both men and women.

Assessment of tidal volume and thoracoabdominal motion using volume and flow-oriented incentive spirometers in healthy subjects

The objective of the present study was to evaluate incentive spirometers using volume- (Coach and Voldyne) and flow-oriented (Triflo II and Respirex) devices. Sixteen healthy subjects, 24 +/- 4 years, 62 +/- 12 kg, were studied. Respiratory variables were obtained by respiratory inductive plethysmography, with subjects in a semi-reclined position (45 masculine). Tidal volume, respiratory frequency, minute ventilation, inspiratory duty cycle, mean inspiratory flow, and thoracoabdominal motion were measured. Statistical analysis was performed with Kolmogorov-Smirnov test, t-test and ANOVA. Comparison between the Coach and Voldyne devices showed that larger values of tidal volume (1035 +/- 268 vs 947 +/- 268 ml, P = 0.02) and minute ventilation (9.07 +/- 3.61 vs 7.49 +/- 2.58 l/min, P = 0.01) were reached with Voldyne, whereas no significant differences in respiratory frequency were observed (7.85 +/- 1.24 vs 8.57 +/- 1.89 bpm). Comparison between flow-oriented devices showed larger values of inspiratory duty cycle and lower mean inspiratory flow with Triflo II (0.35 +/- 0.05 vs 0.32 +/- 0.05 ml/s, P = 0.00, and 531 +/- 137 vs 606 +/- 167 ml/s, P = 0.00, respectively). Abdominal motion was larger (P < 0.05) during the use of volume-oriented devices compared to flow-oriented devices (52 +/- 11% for Coach and 50 +/- 9% for Voldyne; 43 +/- 13% for Triflo II and 44 +/- 14% for Respirex). We observed that significantly higher tidal volume associated with low respiratory frequency was reached with Voldyne, and that there was a larger abdominal displacement with volume-oriented devices.

Reinforcing effects of modafinil: influence of dose and behavioral demands following drug administration

The reinforcing effects of stimulant drugs are modulated by behavioral demands following drug administration. The objective of this study was to assess the reinforcing effects of modafinil, a drug with purportedly low abuse potential, under different behavioral demands using a modified progressive-ratio procedure. The reinforcing effects of oral modafinil (0, 100, 200, and 400 mg) were assessed in six healthy adult volunteers under both performance and relaxation conditions. Performance sessions required volunteers to complete simple arithmetic problems for three 50-min blocks. Relaxation sessions required volunteers to sit quietly in a semi-reclined position in a darkened room for three 50-min blocks. Two sampling sessions (one performance and one relaxation session) always preceded two self-administration sessions (one performance and one relaxation session), and the order of performance and relaxation sessions was constant within a dose condition. Modafinil significantly increased break point and number of capsules earned on the modified progressive-ratio procedure as an increasing function of dose under the performance, but not the relaxation, condition. Modafinil produced comparable stimulant-like subjective ratings under both the performance and relaxation conditions. The findings of the present experiment demonstrate that modafinil can function as a reinforcer and that the reinforcing effects of modafinil are influenced by behavioral demands following drug administration, similar to those of other stimulant drugs.

Effect of active muscle mass during ischemic exercise on peak lower leg vascular conductance

Uncertainty exists as to whether a period of passive arterial occlusion (PAO) or ischemic exercise (IE) results in peak lower leg vascular conductance (LVC). This uncertainty is due to the different body positions, active muscle mass, and occlusion times used for PAO or IE. The purpose of this study was to examine whether 10 min of PAO elicits a similar LVC compared with ischemic dorsiflexion (IDF), ischemic plantar flexion (IPF), and ischemic plantar-dorsiflexion (IPDF). Ten subjects (5 women, 27 +/- 9 yr, 68 +/- 3 kg) were studied on 3 days over 1 wk in a semireclined position with the right foot attached to an isokinetic dynamometer. Mean arterial pressure (Finapres) and lower leg blood flow (LBF, venous occlusion plethysmography) were measured at rest and after PAO and IE. PAO was administered randomly on 1 of the 3 days and before IE. IE protocols consisted of maximal isokinetic dorsiflexion and/or plantar flexion at 120 and 60 degrees/s, respectively. In a second experiment, an additional eight subjects (4 women, 29 +/- 12 yr, 77 +/- 12 kg) were studied to examine the effect of isokinetic speed during IDF on peak LBF and LVC. Peak LVC (ml.min(-1).100 ml(-1).mmHg(-1)) was similar among IPF (0.590 +/- 0.16), IPDF (0.532 +/- 0.17), and PAO (0.511 +/- 0.18), and significantly lower after IDF (0.334 +/- 0.15). No differences in peak LBF and LVC were observed after IDF using different isokinetic speeds. We conclude that 10 min of PAO, IPF, and IPDF performed in a similar posture are adequate stimuli to elicit peak LVC.