Manning J. Sabatier

Concurrent cardiovascular and resistance training in healthy older adults.

PURPOSE The recommendations for exercise training and physical activity for older adults include cardiovascular and resistance training components (CVT and RT, respectively). The purpose of the present investigation was to compare the fitness benefits of concurrent CVT and RT with those attained through an equivalent duration of CVT or RT alone. METHODS Thirty-six participants (ages 60-84) were assigned to a control group or to one of three exercise treatment groups. The treatment groups exercised three times per week for 12 wk using RT (N = 11), CVT (N = 10), or CVT and RT (BOTH, N = 9). Pre- and post-training, participants performed a submaximal exercise test (GXT), five repetition-maximum strength tests (5RM), and the AAHPERD functional fitness test for older adults. RESULTS All exercise treatment groups revealed lower resting heart rate and rate-pressure product; lower exercise diastolic blood pressure and rating of perceived exertion; increased GXT duration; increased leg, back, and shoulder 5RM scores; and improved AAHPERD flexibility, coordination, and cardiovascular endurance scores. The exercise treatment groups responded differently on the following: RT and BOTH enhanced arm and chest strength more than CVT; and BOTH enhanced AAHPERD strength and agility scores more than CVT or RT. CONCLUSIONS Concurrent CVT and RT is as effective in eliciting improvements in cardiovascular fitness and 5RM performance as CVT or RT, respectively. Moreover, incorporating both CVT and RT in exercise programs for older adults may be more effective in optimizing aspects of functional fitness than programs that involve only one component.

Treadmill training promotes axon regeneration in injured peripheral nerves.

Physical activity after spinal cord injury promotes improvements in motor function, but its effects following peripheral nerve injury are less clear. Although axons in peripheral nerves are known to regenerate better than those in the CNS, methods of accelerating regeneration are needed due to the slow overall rate of growth. Therefore we studied the effect of two weeks of treadmill locomotion on the growth of regenerating axons in peripheral nerves following injury. The common fibular nerves of thy-1-YFP-H mice, in which a subset of axons in peripheral nerves express yellow fluorescent protein (YFP), were cut and repaired with allografts from non-fluorescent littermates, and then harvested two weeks later. Mice were divided into groups of low-intensity continuous training (CT, 60 min), low-intensity interval training (IT; one group, 10 reps, 20 min total), and high-intensity IT (three groups, 2, 4, and 10 reps). One repetition consisted of 2 min of running and 5 min of rest. Sixty minutes of CT resulted in the highest exercise volume, whereas 2 reps of IT resulted in the lowest volume of exercise. The lengths of regenerating YFP(+) axons were measured in images of longitudinal optical sections of nerves. Axon profiles were significantly longer than control in all exercise groups except the low-intensity IT group. In the CT group and the high-intensity IT groups that trained with 4 or 10 repetitions axons were more than twice as long as unexercised controls. The number of intervals did not impact axon elongation. Axon sprouting was enhanced in IT groups but not the CT group. Thus exercise, even in very small quantities, increases axon elongation in injured peripheral nerves whereas continuous exercise resulting in higher volume (total steps) may have no net impact on axon sprouting.

Enhancing recovery from peripheral nerve injury using treadmill training.

Full functional recovery after traumatic peripheral nerve injury is rare. We postulate three reasons for the poor functional outcome measures observed. Axon regeneration is slow and not all axons participate. Significant misdirection of regenerating axons to reinnervate inappropriate targets occurs. Seemingly permanent changes in neural circuitry in the central nervous system are found to accompany axotomy of peripheral axons. Exercise in the form of modest daily treadmill training impacts all three of these areas. Compared to untrained controls, regenerating axons elongate considerably farther in treadmill trained animals and do so via an autocrine/paracrine neurotrophin signaling pathway. This enhancement of axon regeneration takes place without an increase in the amount of misdirection of regenerating axons found without training. The enhancement also occurs in a sex-dependent manner. Slow continuous training is effective only in males, while more intense interval training is effective only in females. In treadmill trained, but not untrained mice the extent of coverage of axotomized motoneurons is maintained, thus preserving important elements of the spinal circuitry.

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

Study design:Longitudinal.Objectives:The purpose of this study was to evaluate the effect of lower extremity resistance training on quadriceps fatigability, femoral artery diameter, and femoral artery blood flow.Setting:Academic Institution.Methods:Five male chronic spinal cord injury (SCI) individuals (American Spinal Injury Association (ASIA): A complete; C5–T10; 36±5 years old) completed 18 weeks of home-based neuromuscular electrical stimulation (NMES) resistance training. Subjects trained the quadriceps muscle group twice a week with four sets of 10 dynamic knee extensions against resistance while in a seated position. All measurements were made before training and after 8, 12, and 18 weeks of training. Ultrasound was used to measure femoral artery diameter and blood flow. Blood flow was measured before and after 5 and 10 min of distal cuff occlusion, and during a 4-min isometric electrical stimulation fatigue protocol.Results:Training resulted in significant increases in weight lifted and muscle mass, as well as a 60% reduction in muscle fatigue (P=0.001). However, femoral arterial diameter did not increase. The range was 0.44±0.03 to 0.46±0.05 cm over the four time points (P=0.70). Resting, reactive hyperemic, and exercise blood flow did not appear to change with training.Conclusion:NMES resistance training improved muscle size and fatigue despite an absence of response in the supplying vasculature. These results suggest that the decreases in arterial caliber and blood flow seen with SCI are not tightly linked to muscle mass and fatigue resistance. In addition, muscle fatigue in SCI patients can be improved without increases in arterial diameter or blood flow capacity.Sponsorship:Grants HL65179, HD39676, and HD39676S2.

Upper vs Lower Extremity Arterial Function After Spinal Cord Injury

Abstract Background/Objective: The purpose of the study was to determine whether arterial diameter, flow- mediated dilatation (FMD), and arterial range are affected by spinal cord injury (SCI). We assessed arm (radial) and leg (posterior-tibial) arteries that are comparable in size and function to determine whether (a) arterial function is reduced in individuals with SCI vs nondisabled subjects and (b) decrements to SCI arterial function are greater in the legs vs arms. Participants: Eighteen men with chronic (9.8 ± 6.3 years) SCI (T2 to Til; American Spinal Injury Association A) and 13 nondisabled subjects matched for age (33.1 ± 4.8 vs 29.8 ± 8.2 years old, respectively), height, and weight (BMI = 25.3 ± 5.8 vs 26.6 ± 5.5 kg/m2, respectively). Methods: Radial and posterior tibial artery B-mode ultrasound images were continuously captured to measure resting diameter, occluded diameter, and postischemic diameters. Hierarchical linear modeling accounted for the nested experimental design. Results: Individuals with SCI have lower systemic (arm + leg) FMD than nondisabled subjects (9.3% vs 12.3%, respectively; P= 0.035), primarily because of reduced leg FMD (11.5 ± 3.1 % vs 7.0 ± 2.8% for SCI arms vs legs, respectively; P = 0.010). Persons with SCI also had lower arterial range than nondisabled subjects (0.79 vs 1.00 mm, respectively; P = 0.043), primarily because of the legs (0.81 ± 0.09 vs 0.56 ± 0.11 mm for SCI arms vs legs, respectively; P= 0.030). Conclusion: Leg arterial function seems to deteriorate at greater rates compared to the arms for individuals with SCI. Interventions to improve cardiovascular health should include measurements taken in the legs.

Treadmill training enhances axon regeneration in injured mouse peripheral nerves without increased loss of topographic specificity.

We investigated the extent of misdirection of regenerating axons when that regeneration was enhanced by using treadmill training. Retrograde fluorescent tracers were applied to the cut proximal stumps of the tibial and common fibular nerves 2 or 4 weeks after transection and surgical repair of the mouse sciatic nerve. The spatial locations of retrogradely labeled motoneurons were studied in untreated control mice and in mice receiving 2 weeks of treadmill training, according to either a continuous protocol (10 m/minute, 1 hour/day, 5 days/week) or an interval protocol (20 m/minute for 2 minutes, followed by a 5‐minute rest, repeated four times, 5 days/week). More retrogradely labeled motoneurons were found in both treadmill‐trained groups. The magnitude of this increase was as great as or greater than that found after using other enhancement strategies. In both treadmill‐trained groups, the proportions of motoneurons labeled from tracer applied to the common fibular nerve that were found in spinal cord locations reserved for tibial motoneurons in intact mice were no greater than in untreated control mice and significantly less than those found after electrical stimulation or chondroitinase treatment. Treadmill training in the first 2 weeks following peripheral nerve injury produces a marked enhancement of motor axon regeneration without increasing the propensity of those axons to choose pathways leading to functionally inappropriate targets. J. Comp. Neurol. 517:245–255, 2009.

Electrical stimulation-evoked resistance exercise therapy improves arterial health after chronic spinal cord injury.

Study design:Repeated measures training intervention.Objectives:To evaluate the effects of neuromuscular electrical stimulation (NMES)-induced resistance exercise therapy on lower extremity arterial health in individuals with chronic, complete spinal cord injury (SCI). We define ‘arterial health’ using three surrogate markers: (a) resting diameter, (b) flow-mediated dilation (FMD), and (c) arterial range.Setting:Department of Kinesiology, University of Georgia, USA.Methods:We assessed five 36±5-year-old male individuals with chronic, complete SCI before, during, and after 18 weeks of training. The quadriceps femoris muscle group of both legs were trained twice a week with 4 × 10 repetitions of unilateral, dynamic knee extensions. The health of the posterior tibial artery was assessed using a B-mode ultrasound unit equipped with a high-resolution video capture device. Proximal occlusion was used to evoke ischemia for 5 min and then for 10 min. FMD was calculated using the peak diameter change (above rest) following 5 min occlusion. Arterial range was calculated using minimum (during occlusion) and maximum diameters (post 10 min occlusion). Hierarchical linear modeling accounted for the nested (repeated measures) experimental design.Results:FMD improved from 0.08±0.11 mm (2.7%) to 0.18±0.15 mm (6.6%) (P=0.004), and arterial range improved from 0.36±0.28 to 0.94±0.40 mm (P=0.001), after 18 weeks of training. Resting diameter did not significantly change.Conclusions:Home-based, self-administered NMES resistance exercise therapy consisting of 80 contractions/week improved FMD and arterial range. This provides evidence that resistance exercise therapy can improve arterial health after SCI, which may reduce the risk of future cardiovascular disease.

Misdirection of Regenerating Axons and Functional Recovery Following Sciatic Nerve Injury in Rats

Poor functional recovery found after peripheral nerve injury has been attributed to the misdirection of regenerating axons to reinnervate functionally inappropriate muscles. We applied brief electrical stimulation (ES) to the common fibular (CF) but not the tibial (Tib) nerve just prior to transection and repair of the entire rat sciatic nerve, to attempt to influence the misdirection of its regenerating axons. The specificity with which regenerating axons reinnervated appropriate targets was evaluated physiologically using compound muscle action potentials (M responses) evoked from stimulation of the two nerve branches above the injury site. Functional recovery was assayed using the timing of electromyography (EMG) activity recorded from the tibialis anterior (TA) and soleus (Sol) muscles during treadmill locomotion and kinematic analysis of hindlimb locomotor movements. Selective ES of the CF nerve resulted in restored M‐responses at earlier times than in unstimulated controls in both TA and Sol muscles. Stimulated CF axons reinnervated inappropriate targets to a greater extent than unstimulated Tib axons. During locomotion, functional antagonist muscles, TA and Sol, were coactivated both in stimulated rats and in unstimulated but injured rats. Hindlimb kinematics in stimulated rats were comparable to untreated rats, but significantly different from intact controls. Selective ES promotes enhanced axon regeneration but does so with decreased fidelity of muscle reinnervation. Functional recovery is neither improved nor degraded, suggesting that compensatory changes in the outputs of the spinal circuits driving locomotion may occur irrespective of the extent of misdirection of regenerating axons in the periphery. J. Comp. Neurol. 519:21‐33, 2011.

Sex differences in the effectiveness of treadmill training in enhancing axon regeneration in injured peripheral nerves.

Exercise in the form of daily treadmill training results in significant enhancement of axon regeneration following peripheral nerve injury. Because androgens are also linked to enhanced axon regeneration, we wanted to investigate whether sex differences in the effect of treadmill training might exist. The common fibular nerves of thy‐1‐YFP‐H mice were cut and repaired with a graft of the same nerve from a strain‐matched wild‐type donor mouse. Animals were treated with one of two daily treadmill training paradigms: slow continuous walking for 1 h or four higher intensity intervals of 2 min duration separated by 5‐min rest periods. Training was begun on the third day following nerve injury and continued 5 days per week for 2 weeks. Effects on regeneration were evaluated by measuring regenerating axon profile lengths in optical sections through the repair sites and grafts at the end of the training period. No sex differences were found in untrained control mice. Continuous training resulted in significant enhancement of axon regeneration only in males. No effect was found in females or in castrated males. Interval training was effective in enhancing axon regeneration only in females and not in intact males or castrated males. Untrained females treated with the aromatase inhibitor, anastrozole, had significant enhancement of axon regeneration without increasing serum testosterone levels. Two different mechanisms exist to promote axon regeneration in a sex‐dependent manner. In males treadmill training uses testicular androgens. In females, a different cellular mechanism for the effect of treadmill training must exist.

Effect of slope and sciatic nerve injury on ankle muscle recruitment and hindlimb kinematics during walking in the rat.

Slope-related differences in hindlimb movements and activation of the soleus and tibialis anterior muscles were studied during treadmill locomotion in intact rats and in rats 4 and 10 weeks following transection and surgical repair of the sciatic nerve. In intact rats, the tibialis anterior and soleus muscles were activated reciprocally at all slopes, and the overall intensity of activity in tibialis anterior and the mid-step activity in soleus increased with increasing slope. Based on the results of principal components analysis, the pattern of activation of soleus, but not of tibialis anterior, changed significantly with slope. Slope-related differences in hindlimb kinematics were found in intact rats, and these correlated well with the demands of walking up or down slopes. Following recovery from sciatic nerve injury, the soleus and tibialis anterior were co-activated throughout much of the step cycle and there was no difference in intensity or pattern of activation with slope for either muscle. Unlike intact rats, these animals walked with their feet flat on the treadmill belt through most of the stance phase. Even so, during downslope walking limb length and limb orientation throughout the step cycle were not significantly changed from values found in intact rats. This conservation of hindlimb kinematics was not observed during level or upslope walking. These findings are interpreted as evidence that the recovering animals adopt a novel locomotor strategy that involves stiffening of the ankle joint by antagonist co-activation and compensation at more proximal joints. Their movements are most suitable to the requirements of downslope walking but the recovering rats lack the ability to adapt to the demands of level or upslope walking.