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Biomedical subjects

G J Bell

Publications and source records attributed to G J Bell.

At least 19 recordsLinked to original sources
PubMed2004

Modification of the Wingate anaerobic power test for rowing: optimization of the resistance setting.

The purpose of the study was to determine the resistance factor that would elicit the highest peak 5 s and mean 30 s power output (PO) during a maximal 30 s anaerobic power test on a rowing ergometer. Thirty-one rowers (17 male and 14 female) were recruited based on the light-weight (LW) (6 male; age 23 +/- 6 yrs and 6 female; age 19 +/- 2 yrs) and heavy-weight (HW) (11 male; age 24 +/- 4 yrs and 8 female; age 27 +/- 8 yrs) rowing categories. Each group completed 5 randomized series of maximal 30 s sprints equivalent to the following forces: 58.9, 63.8, 68.7, 73.7 and 78.6 N for LW males; 83.5, 88.4, 93.4, 98.2 and 103.1 N for HW males; 29.4, 34.3, 39.2, 44.1 and 49.1 N for LW females; and 44.1, 49.1, 54.0, 58.6 and 63.8 N for HW females. The tests were performed on a Gjessing rowing ergometer modified to accommodate greater resistance settings and computer linked to obtain the necessary data. The peak 5 s and mean 30 s PO (W) were determined for each test. A relative load factor (RLF) for determining the amount of resistance to be applied was calculated based on body mass (BM). The RLF settings that elicited the highest peak 5 s PO were 0.109 and 0.102 kg. kg (-1) BM for LW and HW male rowers and 0.111 kg. kg (-1) BM and 0.076 kg. kg (-1) BM for LW and HW female rowers, respectively. The RLF settings for eliciting the highest mean 30 s PO were 0.102 and 0.095 kg. kg (-1) BM for LW and HW male rowers and 0.103 kg. kg (-1) BM and 0.068 kg. kg (-1) BM for LW and HW female rowers, respectively. A 30 second anaerobic test was also performed on a Concept II rowing machine for comparison and it was found to elicit a significantly lower peak 5 s but not 30 s PO in both male and female rowers. Our findings provide RLFs for assessing anaerobic power using a 30 s test in male and female rowers. As well, peak 5 s but not mean 30 s PO is underestimated using the Concept II rowing machine.

Adult↗
PubMed2002

The effect of concurrent endurance and strength training on quantitative estimates of subsarcolemmal and intermyofibrillar mitochondria.

We examined the effect of combined strength and endurance training on quantitative estimates of mitochondria in subsarcolemmal and intermyofibrillar regions of muscle fibers. Ten subjects (five males, five females) participated in a 12 week program of combined strength and endurance training. Seven subjects (three males and four females) served as controls. Biopsy samples from the vastus lateralis were obtained before and after training in both groups and also at the mid-point of training in the exercise group. Measurement of succinate dehydrogenase activity throughout muscle fibers, as a quantitative estimate of mitochondrial subpopulations, revealed no differences between exercise and control groups before and after training. Within the exercise group, there was a significant increase in succinate dehydrogenase activity in all regions of muscle fibers from before to after training. There was also a significant increase in succinate dehydrogenase activity in the subsarcolemmal, relative to the intermyofibrillar region from mid-(six weeks) to after-training ( regional distribution x time; p < 0.05). This may have been associated with an oxidative shift in fiber types, as type I fiber percentage was increased in the exercise, compared to the control group (group x time; p < 0.05). We conclude that mitochondrial populations undergo differential changes throughout training. IMF mitochondria increase in a linear manner throughout training, while SS mitochondria undergo a preferential increase late in training. This increase late in training may be related to an increase in proportion of type I fibers.

Adaptation, Physiological↗
PubMed2001

Improved efficiency with a wheelchair propelled by the legs using voluntary activity or electric stimulation.

OBJECTIVE: To determine whether a new leg-propelled wheelchair provides enhanced efficiency and mobility to wheelchair users. DESIGN: Observational; subjects were tested while wheeling with the arms and legs and while walking (where possible) for 4-minute periods in random order with approximately 10-minute rest periods between exercise sets. SETTING: Tests were done on an indoor 200-meter track. PATIENTS: Group 1, 13 controls; group 2, 9 persons with complete spinal cord injury (SCI); group 3, 13 persons with other motor disorders (retaining some voluntary control of the legs). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Physiological Cost Index (PCI), (computed as change in heart rate divided by velocity of movement) and oxygen consumption (VO(2)) RESULTS: Arm wheeling took significantly more effort (mean PCI =.52 beats/m) than walking (.33 beats/m) in control subjects. Leg wheeling was most efficient (.23), requiring less than half the effort of arm wheeling and 30% less effort than walking. For SCI subjects, leg wheeling with functional electric stimulation (FES) required less than half the effort (.18) of arm wheeling (.40). The FES group could not walk. Subjects in group 3 could walk, but with substantial effort (1.81) compared with arm (.76) or leg wheeling (.64). Results for VO(2) were similar. CONCLUSIONS: Better wheelchair efficiency can be obtained for many disabled individuals, by moving the leg muscles voluntarily or with FES.

Adult↗
PubMed2001

Effects of creatine monohydrate supplementation during combined strength and high intensity rowing training on performance.

This study investigated the effect of creatine monohydrate (Cr) supplementation on performance and training volume in rowers. Twenty-two rowers trained with continuous and interval rowing and resistance training 4 and 2 days/week, respectively, for 6 weeks. Cr supplementation consisted of a 5-day load (0.3 g/kg(-1) x day(-1)) followed by a 5-week maintenance dose (0.03 g/kg(-1) x day(-1)) while training. Five days of Cr loading did not change body composition, repeated interval rowing performance, 2,000-m rowing times, or strength performance. Five additional weeks of training with a maintenance dose of Cr or placebo significantly improved body composition, VO2max, 2,000-m rowing times, repeated power interval performance, and strength to a similar extent in both groups. Subjects training with Cr did not perform more repetitions per set of strength exercise nor produce or maintain higher power outputs during repeated rowing sessions. Cr supplementation did not increase performance or training volume over a placebo condition in rowers that performed a combined high intensity rowing and strength program.

Adult↗
PubMed2000

Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans.

The purpose of this study was to investigate the effect of concurrent strength and endurance training on strength, endurance, endocrine status and muscle fibre properties. A total of 45 male and female subjects were randomly assigned to one of four groups; strength training only (S), endurance training only (E), concurrent strength and endurance training (SE), or a control group (C). Groups S and E trained 3 days a week and the SE group trained 6 days a week for 12 weeks. Tests were made before and after 6 and 12 weeks of training. There was a similar increase in maximal oxygen consumption (VO2max) in both groups E and SE (P < 0.05). Leg press and knee extension one repetition maximum (1 RM) was increased in groups S and SE (P < 0.05) but the gains in knee extension 1 RM were greater for group S compared to all other groups (P < 0.05). Types I and II muscle fibre area increased after 6 and 12 weeks of strength training and after 12 weeks of combined training in type II fibres only (P < 0.05). Groups SE and E had an increase in succinate dehydrogenase activity and group E had a decrease in adenosine triphosphatase after 12 weeks of training (P < 0.05). A significant increase in capillary per fibre ratio was noted after 12 weeks of training in group SE. No changes were observed in testosterone, human growth hormone or sex hormone binding globulin concentrations for any group but there was a greater urinary cortisol concentration in the women of group SE and decrease in the men of group E after 12 weeks of training (P < 0.05). These findings would support the contention that combined strength and endurance training can suppress some of the adaptations to strength training and augment some aspects of capillarization in skeletal muscle.

Adult↗
PubMed2000

A comparison of critical velocity estimates to actual velocities in predicting simulated rowing performance.

The most accurate critical velocity (CV) estimate for the prediction of velocity during a simulated 2,000-m rowing race and the relationship to aerobic power were studied. Sixteen male rowers completed randomized maximal exertion trials (200, 400, 600, 800, 1,000, and 1,200 m), a maximal oxygen consumption (VO(2)max) on a Concept II rowing machine, and an actual 2,000-m simulated rowing race. Three mathematical models were applied to 4 rowing distance combinations producing 12 CV estimates. Seven of the 12 possible CV estimates were not significantly different from actual 2,000-m velocity. Comparison of the 3 CV models using all 6 trial distances revealed that the nonlinear model produced a CV estimate lower than the 2 linear CV models. CV was significantly correlated to VO(2)max (r = 0.91) and the mean velocity achieved during the 2,000-m simulated rowing race (r = 0.97). VO(2)max was significantly correlated to 2,000-m simulated rowing race velocity (r = 0.93).

Adult↗
PubMed1998

Higher mitochondrial fatty acid oxidation following intermittent versus continuous endurance exercise training.

It has been well documented that skeletal muscle fatty acid oxidation can be elevated by continuous endurance exercise training. However, it remains questionable whether similar adaptations can be induced with intermittent interval exercise training. This study was undertaken to directly compare the rates of fatty acid oxidation in isolated subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria following these different exercise training regimes. Mitochondria were isolated from the gastrocnemius-plantaris muscles of male Sprague-Dawley rats following exercise training 6 days per week for 12 weeks. Exercise training consisted of either continuous, submaximal, endurance treadmill running (n = 10) or intermittent, high intensity, interval running (n = 10). Both modes of training enhanced the oxidation of palmityl-carnitine-malate in both mitochondrial populations (p < 0.05). However, the increase associated with the intermittent, high intensity exercise training was significantly greater than that achieved with the continuous exercise training (p < 0.05). Also, the increases associated with the IMF mitochondria were greater than the SS mitochondria (p < 0.05). These data suggest that high intensity, intermittent interval exercise training is more effective for stimulation of fatty acid oxidation than continuous submaximal exercise training and that this adaptation occurs preferentially within IMF mitochondria.

Adenosine Triphosphatases↗
PubMed1998

The effect of aerobic exercise training on the distribution of succinate dehydrogenase activity throughout muscle fibres.

We evaluated the effect of endurance training (cycling 3 times per week for 12 weeks) on succinate dehydrogenase (SDH) activity in the subsarcolemmal (SS) and intermyofibrillar (IMF) regions of vastus lateralis muscle fibres in 7 individuals (4 females and 3 males). SDH activity of the SS region increased 9.4% and 12.8% in type I and II fibres, respectively (p < .05). SDH activity of the IMF region increased 4.7% and 6.7% in type I and II fibres, respectively (p < .05). This was less than the increase in the SS region (p < .05). No significant changes were observed in a control group (4 females and 3 males). These data suggest that mitochondria in the SS and IMF regions of human vastus lateralis muscle fibres are sensitive to endurance training. The greater response in the SS region suggests that the metabolic requirements of SS mitochondria were stressed to a greater extent than IMF mitochondria with endurance training.

Adult↗
PubMed1998

Exercise after acute hyperbaric oxygenation: is there an ergogenic effect?

The purpose of this study was to determine the effects of a 1-h exposure to 2.0 atm abs (202.6 kPa) and 100% oxygen on subsequent maximal O2 consumption (VO2max), ventilation threshold (VT), lactate threshold (LT), and muscle oxygenation (%Mox) during incremental exercise to maximum on a cycle ergometer. Two baseline exercise tests (T1 and T2) were performed on separate occasions without prior exposure to hyperbaric oxygen (HBO2) and a third test (T3-HBO2) was performed after (22.5 +/- 5.6 min) HBO2 Near infared spectroscopy was used to monitor oxygenation of the left vastus lateralis muscle during T2 and T3-HBO2. No significant differences were observed between VO2max VT, or LT among any of the exercise tests. There was no significant difference in %Mox between T2 and T3-HBO2 except at 235 W where there was a significant elevation in %Mox during T3-HBO2 relative to T2. These results suggest that prior exposure to HBO2 (100% O2 at 2 atm abs for 1 h) has no ergogenic effect on subsequent incremental exercise performance.

Adult↗
PubMed1997

Relationship between aerobic fitness and metabolic recovery from intermittent exercise in endurance athletes .

This investigation examined the relationship between several different aerobic fitness test results and measurements of metabolic recovery from intermittent, high-intensity exercise in 16 male cyclists. No significant correlations were found between maximal oxygen consumption, ventilation threshold, various submaximal endurance measures and the rate of metabolic recovery, net excess postexercise oxygen consumption, or blood lactate removal after intermittent high-intensity exercise except for submaximal heart rate (r = .66, p < .05). These data indicate that aerobic fitness assessments do not indicate the ability to recover after intermittent, high-intensity exercise in endurance-trained cyclists.

Adult↗
PubMed1993

Maintenance of strength gains while performing endurance training in oarswomen.

This study investigated the retention of strength gained after resistance training, while performing aerobic endurance training. Following a 10-week resistance training program (three times a week) that included maintenance aerobic endurance training (twice a week), 18 varsity oarswomen were matched on strength and randomly assigned to two groups: Group 1 performed maintenance resistance training once a week and Group 2 performed resistance training twice a week. Both groups performed endurance training four times a week during the 6-week maintenance resistance training program. There was a significant increase in strength (multiple-RM test) for three upper and three lower body exercises after the initial 10-week resistance training program. A further significant increase in two exercises (inclined leg press and knee flexion) were observed after 6 weeks of maintenance resistance training and endurance training in both groups. No further significant increases were observed in the four other exercises during maintenance strength training. These latter findings occurred at the same time that VO2max and ventilation threshold increased. These results suggest that strength gains can be maintained with resistance training once or twice a week while focusing on improving aerobic endurance performance without compromising the latter.

Adult↗
PubMed1992

Recovery of rat tibialis anterior motor unit properties following partial denervation.

The recovery of selected mechanical, morphological, and metabolic properties of rat tibialis anterior fast motor units was determined following partial denervation (n = 7) or partial denervation and hemispinal cord transection (n = 5) and compared with age-matched control units (n = 7). Following 1-12 months of recovery, the mechanical properties of each unit were measured and the fibres depleted of glycogen by using standard ventral root filament stimulation techniques. Quantitative histochemical techniques were used to determine cross-sectional area and the activities of succinate dehydrogenase and alpha-glycerolphosphate dehydrogenase in individual unit fibres. Partial denervation increased the mean fibre area but decreased alpha-glycerolphosphate dehydrogenase activity. Succinate dehydrogenase was unchanged in the denervated groups. The variability in area and enzymatic activities among the unit fibres was unchanged. However, the interrelationship between the enzymes was altered by both denervation procedures. Succinate dehydrogenase activity was directly related to fatigue resistance and inversely related to tetanic tension across the units. These findings suggest that a motor unit reestablishes many of its properties despite marked changes to the composition of the unit brought about by partial denervation. In addition, a reduction in the neuromuscular activity of units during reorganization had a limited effect on recovery.

Animals↗
PubMed1992

Altered distribution of mitochondria in rat soleus muscle fibers after spaceflight.

The influence of spaceflight on the distribution of succinate dehydrogenase (SDH) activity throughout the cross section of fibers in the soleus was studied in five male rats and in five rats maintained under ground-based simulated flight conditions (control). The flight (COSMOS 1887) was 12.5 days in duration, and the animals were killed approximately 2 days after return to 1 G. Fibers were classified as slow-twitch oxidative or fast-twitch oxidative-glycolytic in histochemically prepared tissue sections. The distribution of SDH activity throughout the cross section of 20-30 fibers (each type) was determined using quantitative histochemical and computer-assisted image analysis techniques. In all the fibers, the distribution of SDH activity was significantly higher in the subsarcolemmal than in intermyofibrillar region. After spaceflight the entire regional distribution of SDH activity was significantly altered in the slow-twitch oxidative fibers. The fast-twitch oxidative-glycolytic fibers of the spaceflight muscles exhibited a significantly lower SDH activity only in their subsarcolemmal region. These data suggest that when determining the influence of spaceflight on muscle fiber oxidative metabolism enzymes, it is important to consider the location of the enzyme throughout the cross section of a fiber. Furthermore the functional properties of the soleus that depend on the metabolic support of mitochondria in the subsarcolemmal region may be primarily affected by exposure to microgravity.

Animals↗
PubMed1992

Physiological adaptations to velocity-controlled resistance training.

The force-velocity characteristics of skeletal muscle are such that maximal force is inversely related to the velocity of shortening. This relationship has been observed using isolated muscle preparations and intact muscle groups (e.g. knee extensors). Isokinetic dynamometry has revealed some specific physiological adaptations to different velocities of training: an increase in torque and power that are greater at or near the velocity of training; a transfer of torque gains to slower and faster angular velocities after intermediate velocity resistance training; increases in maximal oxygen consumption and cardiac output in response to circuit training; increases in anaerobic power output; changes in skeletal muscle size and changes in myofibrillar ATPase activity; and new applications for rehabilitation of muscular and ligamentous injuries, and post-coronary patients.

Adaptation, Physiological↗
PubMed1992

Effect of high velocity resistance training on peak torque, cross sectional area and myofibrillar ATPase activity.

The purpose of this investigation was to determine the effect of high velocity resistance (HVR) training on peak torque (PT), cross sectional area (CSA) and myofibrillar ATPase activity of the knee extensors. HVR training was performed in a circuit on hydraulic exercise equipment, 4 times a week for 5 weeks at an angular velocity of approximately 3.14 rad.s-1. Knee extension PT was determined on a Cybex II isokinetic dynamometer and CSA of the quadriceps femoris muscle was assessed using computer tomography (CT) scanning. Muscle biopsies were obtained from the lateral quadriceps muscle and were analyzed for myofibrillar ATPase activity. Knee extension peak torque was significantly increased at 1.57, 2.09, 3.14, 3.66 and 4.19 rad.s-1. Myofibrillar ATPase activity and CSA was also significantly increased after HVR training. These findings showed that short-term high velocity resistance training enhances the in vivo torque/velocity curve especially at fast angular velocities and these changes are partly attributed to an increase in muscle CSA and activity of myofibrillar ATPase.

Adaptation, Physiological↗
PubMed1991

Physiological adaptations to concurrent endurance training and low velocity resistance training.

This study investigated the effects of concurrent endurances and low velocity resistance training (LVR) on measures of strength and aerobic endurance. One group (ES) performed concurrent endurance training 3 days a week and LVR training on alternate days, 3 days a week for 12 weeks. The other group (S) performed only LVR training 3 days a week for 12 weeks without any endurance training. Measurements and increases in training volume were made every three weeks in both groups. Group ES exhibited increases in submaximal exercise responses after 3, 9 and 12 weeks (p less than 0.05). Knee extension peak torque and total work as well as cross-sectional area of quadriceps femoris were significantly increased after 6 and 9 weeks of training in both groups. These findings indicate that no significant differences in strength gains were observed between subjects performing concurrent endurance and resistance training or resistance training only. However, the time-course of adaptations between groups was somewhat different.

Adaptation, Physiological↗
PubMed1991

Adaptations to endurance and low velocity resistance training performed in a sequence.

The purpose of this study was to examine the effects of two different sequences of the same two training programs on strength and endurance adaptations. One group completed 5 weeks of low velocity resistance (LVR) training prior to 5 weeks of endurance training (Group SE) while the other group (ES) completed the opposite sequence. Endurance training and resistance training resulted in anticipated increases in aerobic endurance measures and strength, respectively, regardless of the sequence followed. Some maintenance of strength was observed during subsequent endurance training in Group SE. However, the improvements in peak VO2 and submaximal exercise responses that occurred after endurance training in Group ES were not maintained with subsequent LVR training. This investigation suggests that conducting LVR training prior to endurance training may be more beneficial if resistance and endurance training are performed in a sequence.

Adult↗