«BOOK OF ABSTRACTS Edited by: Loland, S., Bø, K., Fasting, K., Hallén, J., Ommundsen, Y., Roberts, G., Tsolakidis, E. Hosted by: The Norwegian ...»
Support: Danish Medical Research Council, Novo Nordisk Foundation, Lundbeck Foundation 08:30 - 10:00 Invited symposia IS-BM08 Laterality and assymetries in sports
MECHANISMS UNDERLYING FUNCTIONAL CHANGES IN THE PRIMARY MOTOR CORTEX IPSILATERAL TO AN ACTIVEARM PEREZ, M.A.
UNIVERSITY OF PITTSBURGHPerformance of a unimanual motor task results in functional changes in both primary motor cortices (M1s). The neuronal mechanisms controlling the corticospinal output originating in the M1 ipsilateral to a moving arm remain poorly understood (1). Gaining insight into these mechanisms may contribute to a better understanding of how unimanual and bimanual movements are controlled (2,3,4,5).
During this presentation I will review several electrophysiological markers of motor cortical function measured at rest and during different levels of unilateral and bilateral finger, wrist and elbow voluntary movements by using transcranial magnetic stimulation (TMS). These electrophysiological markers include: motor-evoked potential (MEP) recruitment curves, short-interval intracortical inhibition (SICI), interhemispheric inhibition measured by a paired-pulse TMS paradigm and by the ipsilateral cortical silent period (iSP), and the influence of interhemispheric inhibition over SICI.
Our results have shown activity-dependent changes in SICI in M1 ipsilateral, interhemispheric inhibition from M1 contralateral to M1 ipsilateral, and in the influence of interhemispheric inhibition over SICI. Differences are observed between responses evoked from distal and proximal representations in the primary motor cortex (4,5). Altogether our findings indicate that interactions between GABAergic intracortical circuits mediating SICI and interhemispheric glutamatergic projections between M1s partly contribute to control activitydependent changes in corticospinal output in the M1 ipsilateral to a moving arm during voluntary movement by the opposite arm.
1. Carson RG. Brain Res Brain Res Rev 49:641–662, 2005
2. Hortobágyi et al. J Neurophysiol 90: 2451-2459, 2003
3. Muellbacher W et al. Clin Neurophysiol 111: 344-349, 2000
4. Perez and Cohen. J Neurosci 28: 5631-5640, 2008
5. Perez and Cohen. Cortex (in press), 2009
MECHANISMS OF CHANGES IN EXCITABILITY OF THE PRIMARY MOTOR CORTEX DURING UNILATERAL MUSCLE CONTRACTIONS: IMPLICATIONS FOR CROSS EDUCATIONHORTOBÁGYI, T., HOWATSON, G., RIDER, P., SOLNIK, S., DEVITA, P.
EAST CAROLINA UNIVERSITYThere is strong evidence suggesting that unilateral exercise increases motor function not only in the muscles of the exercised limb but also in the homologous unexercised muscles of the contralateral limb, producing the phenomenon of cross education (10, 13). Such adaptations occur under a variety of conditions, including exercise with voluntary isometric, concentric, eccentric, and electrical stimulation-evoked contractions (2, 4, 8, 11). The mechanisms of these adaptations are unknown but most likely reside in the nervous system and not in the contralateral muscle itself (1, 3). The purpose of this presentation is to examine candidate mechanisms of cross education in the motor cortex and spinal cord. One possible mechanism is that neural drive in the “uninvolved” motor cortex increases due to its repeated activation during unilateral muscle contractions (7, 12, 14). The magnitude and specificity of cross education are probably related to the magnitude of activation of the ipsilateral motor cortex, which was shown to increase with intensity (7, 9, 12) and vary by type (shortening vs lengthening) (5) of contralateral muscle contraction as determined by magnetic brain stimulation. Another possibility is that chronic exercise reduces interhemispheric inhibition and the increased cross-hemispheric flow in turn increases the excitability of the uninvolved motor cortex (6). Finally, spinal mechanisms cannot be excluded but evidence for cross-segmental effects appears weak or our methods are inadequate to detect such effects (7, 9). In conclusion one of several independent mechanisms or perhaps a combination of these may mediate increased motor output in the unexercised muscles of the contralateral limb after chronic unilateral exercise. After identifying the exact mechanisms of cross education the next step is to determine if it is an effective method for the rehabilitation of unilateral movement impairments in patients with a stroke or unilateral orthopedic injuries.
Supported in part by NIH AG024161
1. Carroll TJ et al. J Appl Physiol 101: 1514-1522, 2006
2. Farthing JP et al. Brain Topogr 20: 77-88, 2007
3. Hortobágyi T IEEE Eng Med Biol Mag 24: 22-28, 2005
4. Hortobágyi T et al. Med. Sci. Sports Exerc. 29: 107-112, 1997
5. Hortobágyi T et al. ACSM. Seattle, WA, May 27-30, 2009
6. Hortobágyi T et al. J Neurosci, Submitted, 2009
7. Hortobágyi T et al. J Neurophysiol 90: 2451-2459, 2003
8. Howatson G et al. Eur J Appl Physiol 101: 207-214, 2007
9. Muellbacher W et al. Clin Neurophysiol 111: 344-349, 2000
10. Munn J et al. J Appl Physiol 96: 1861-1866, 2004
11. Munn J et al. J Appl Physiol 99: 1880-1884, 2005
12. Perez MA et al. J Neurosci 28: 5631-5640, 2008
13. Zhou S. Exerc Sport Sci Rev 28: 177-184, 2000
14. Zijdewind I et al. J Neurophysiol 85: 1907-1913, 2001
NEW PERSPECTIVES ON CROSS EDUCATION: IS THERE A POTENTIAL BENEFIT OF UNILATERAL TRAINING DURING RECOVERY FROM UNILATERAL SPORTS INJURIES?FARTHING, J.P.
UNIVERSITY OF SASKATCHEWANCross education is the strength increase observed in the untrained contralateral limb after a period of unilateral strength training. Although cross education was first documented over a century ago, there is still much to learn regarding the precise neural mechanisms that control the effect and the potential utility of it during recovery from unilateral injury (1,5). Cross education is evident after a variety of unilateral training regimens with an average magnitude of 8% or about half of the strength gain observed in the trained limb (1,8). However the effect varies immensely, ranging from no significant effect up to 77% after voluntary training (6,11). There is now evidence that cross education is asymmetrical, where dominant arm training elicits much greater cross education than non-dominant training in righthanded individuals (2). This suggests that there is a preferential dominant to non-dominant direction of strength transfer in the upper limbs, which might explain some of the variation in the literature regarding the magnitude of effect. This asymmetrical transfer of strength is similar to what has been shown for cross education of skills and suggests involvement of higher order motor learning mechanisms (1,2,7). A follow-up functional MRI study provided initial evidence of changes in brain activation patterns associated with the untrained left limb, particularly in sensorimotor cortex and temporal lobe (3). While several studies have aimed to reveal mechanisms, there are few attempts to apply cross education in a rehabilitation setting (9, 10). The purpose of this presentation is to discuss the potential for cross education to be used as a strategy during rehabilitation from unilateral injuries (particularly those requiring immobilization) and to discuss the implications of asymmetry of cross education in this context. A recent study demonstrated that unilateral strength training was effective for preserving strength in an opposite immobilized limb (4). These findings suggest that there might be a therapeutic benefit of cross education during recovery from unilateral sport injuries or in other clinical settings that involve unilateral immobilization.
Supported by the Saskatchewan Health Research Foundation (SHRF)
1. Carroll TJ et al. J Appl Physiol 101: 1514-1522, 2006 2. Farthing JP et al. Med Sci Sports Exerc 37: 1594-1600, 2005 3. Farthing JP et al.
Brain Topogr 20: 77-88, 2007 4. Farthing JP et al. J Appl Physiol In Press, 2009 5. Hortobágyi T IEEE Eng Med Biol Mag 24: 22-28, 2005 6.
Hortobágyi T et al. Med Sci Sports Exerc 29: 107-112, 1997 7. Lee M and Carroll TJ. Sport Med 37: 1-14, 2007 8. Munn J et al. J Appl Physiol 96: 1861-1866, 2004 9. Stromberg B. Am J Phys Med 65: 135-143, 1986 10. Stromberg B. South Med J 81: 989-991, 1988 11. Zhou S. Exerc Sport Sci Rev 28: 177-184, 2000.
08:30 - 10:00 Oral presentations OP-PH07 Physiology 7
AGING AND RESISTANCE TRAINING INDUCED INCREASE IN MUSCLE SIZEHULMI, J.J., SALMIJÄRVI, H., KATAJAVUORI, M., AHTIAINEN, J.P., HOLVIALA, J., SELÄNNE, H., KOVANEN, V., HÄKKINEN, K., MERO, A.A.
UNIVERSITY OF JYVÄSKYLÄIntroduction: Resistance training (RT) increases muscle size but aging may (5) or may not (1) decrease this response. The present study investigated muscle hypertrophy and gene expression adaptations to heavy RT in young and old healthy men.
Methods Twenty-one previously untrained young men (26.0+-4.3 yrs) and 18 older men (61.2+-4.1) participated in a 21-week RT period, comprising whole-body exercises twice a week. The training loads increased from 60 to 85% of 1RM, and the number of repetitions in each set decreased from 15-20 to 5-6 during RT. Nineteen men (42.5+-20.0) served as controls (no RT). Vastus lateralis (VL) muscle fiber crosssectional area (CSA), expression of muscle hypertrophy regulating genes (by Real-Time RT-PCR), and muscle force were analysed before and after the 21-week period. Muscle biopsies were obtained 4-6 days after the last RT workout. Macronutrient intake was not controlled but it was registered by 4-day diaries at weeks 0, 10.5 and 21.
Results: RT led to 1.2-1.4 -fold increases in strength of leg extensors and muscle fiber CSA (P0.05). Concentric leg extension 1RM increased similarly in young and old whereas isometric leg extension force increased more in young men (P0.05). Type-I and mean (type I+II) muscle fiber CSA increased two times more in young men (P0.05). Young men habitually ingested 1.3-1.4 times more energy and protein per body mass during RT than old men (P0.05). Basal mRNA response to RT of activin receptor IIb, FLRG, MyoD, myogenin, p21, cdk2 and MAFbx were not different between young and old. However, myostatin and myogenin mRNA increased in old compared to young men (P0.05).
Discussion: Larger muscle hypertrophy took place after RT in the young men. The present twice weekly heavy whole body RT may have been too demanding for some previously untrained older individuals. This may have been associated with relatively lower energy and protein intake observed in the old men. Protein and energy undernutrition among the elderly is common (3) and may be especially problematic with RT that increases need for dietary protein (4). On the other hand, it is also possible that the adaptation capacity to RT simply decreases with increasing age. It can be speculated that the increase in muscle myostatin gene expression in the old compared to the young could be related to the observed smaller muscle hypertrophy in the old, as myostatin is a negative regulator of muscle size (2).
In conclusion, aging decreased the enlargement of muscle size during 21 weeks of training. This may be explained by smaller protein and energy ingestion or by an increase in myostatin gene expression in the old.
1. Häkkinen K, et al. JGBSMS 53:B415-23, 1998
2. McPherron AC and Lee SJ. PNAS 94:12457-12461, 1997
3. Sullivan DH, et al. JAMA 281:2013-2019, 1999
4. Tarnopolsky MA, et al. JAP 73:1986-1995, 1992
5. Welle S, et al. JGBSMS 51:M270-5, 1996