Chronic Musculoskeletal Adaptations to Exercise
Original Editor - Wanda van Niekerk based on the course by James Laskin
Top Contributors - Wanda van Niekerk and Jess Bell
Effects of Deconditioning[edit | edit source]
Deconditioning or detraining refers to changes in the body that occur after a period of inactivity. These changes occur in the heart, lungs and muscles. The effects of detraining on body systems[1] are summarised in Table 1.
Neuromuscular | Cardiorespiratory | Musculoskeletal |
---|---|---|
↓ EMG activity
↓mean muscle fibre cross-sectional area ↓ flexibility ↓ muscle strength and power ↓ muscle mass |
↓ maximal oxygen uptake
↑ mean blood pressure ↑ submaximal heart rate ↓ maximal cardiac output ↓ lactate threshold ↓ endurance performance ↓ blood volume ↓ plasma volume ↓ heart volume ↓ orthostatic tolerance |
↓ up to 2.5% in bone mineral density
↓ oxidative enzymes activity ↓ glycogen synthase activity ↓ mitochondrial ATP production ↓ tendon quality |
Read more: The effect of detraining on body systems and the evidence for the effects of detraining.
Common Training Principles[edit | edit source]
- Reversibility principle:
- benefits of training are transient and reversible[3]
- after 2 weeks of detraining there is a measurable reduction in work capacity
- Overload principle:
- a system must be exercised at a level beyond which it is presently accustomed to for a training effect to occur[4]
- Specificity principle:
- Individuality:
- there is variation in response to a training programme as individuals respond differently to the same training programme[4]
Read more: Common Training Principles.
Musculoskeletal Adaptations to Exercise[edit | edit source]
Resistance Training[edit | edit source]
- Resistance training yields substantial strength gains via neuromuscular changes[6]
- Important for overall fitness and health[6]
- Critical for athletic training programmes[7]
Gains in Muscular Fitness[edit | edit source]
- After 3 to 6 months of resistance training, there is:
- Strength gains result from[6]:
- increased muscle size
- altered neural control
Mechanisms of Muscle Strength Gains[edit | edit source]
Neural Control[edit | edit source]
- Strength gains cannot occur without neural adaptations via plasticity[9][10]
- Strength gains can occur without hypertrophy
Read more: The knowns and unknowns of neural adaptations to resistance training.[10]
Neural adaptations[edit | edit source]
- Increased central drive (from the higher centres of the brain) after resistance training is partly responsible for the increase in strength[11]
- Increased motor unit (MU) synchronisation (i.e. several motor units firing at similar times)[12][10]
- Decrease in the force threshold at which motor units are recruited[13]
- Increased motor unit firing rate[14]
- Decrease in the level of co-activation of antagonist muscles after training[15]
Strength Training Model[edit | edit source]
Please refer back to the course video, Chronic Adaptations to Exercise - Musculoskeletal, for a detailed discussion of these concepts. In summary:
- hypertrophy
- neurological changes with resistance training occur predominantly in the early phases of a training programme
- strength
- strong, rapid gains in strength occur relatively quickly and consistently
- over time, improvements in strength reach a plateau
The video below provides a good explanation of neural adaptations to resistance exercise, strength and hypertrophy.
Motor Unit Recruitment[edit | edit source]
Motor unit = efferent neuron and all of the muscle fibres that it innervates.
- Normally motor units are recruited asynchronously
- Synchronous recruitment leads to strength gains:[12]
- facilitates contraction
- may produce more forceful contraction
- improves rate of force development
- increased capability to exert steady forces
- Resistance training leads to synchronous recruitment[19]
- Strength gains may also result from greater motor unit recruitment[10]
- It is likely that some combination of improved motor unit synchronisation and motor unit recruitment results in strength gains[20]
Read more: Motor Units.
Autogenic Inhibition[edit | edit source]
- Normal intrinsic inhibitory mechanisms:
- Resistance training can gradually decrease or counteract inhibitory impulses:[23]
Muscle Hypertrophy[edit | edit source]
- Hypertrophy = increase in muscle mass and cross-sectional area[24]
- Transient hypertrophy (after a single exercise bout) - the "pumping-up" of muscle that happens during a resistance training session
- this is due to oedema formation from plasma fluid[25]
- it disappears within hours
- Chronic hypertrophy (long term)[26]
- reflects actual structural change in muscle
- fibre hypertrophy, fibre hyperplasia, or both
Fibre Hypertrophy[edit | edit source]
- More myofibrils
- More actin, myosin filaments
- More sarcoplasma[27]
- More connective tissue
- Resistance training results in an increase in protein synthesis:[28]
- muscle protein content is always changing
- during exercise, there is a decrease in protein synthesis, and increased degradation
- after exercise, there is an increase in protein synthesis, and decrease in protein degradation[29]
- read more: muscle protein synthesis
- Testosterone facilitates fibre hypertrophy:[30]
- natural anabolic steroid hormone
- synthetic anabolic steroid use results in a large increase in muscle mass
Fibre Hyperplasia[edit | edit source]
Hyperplasia refers to an increase in the number of cells or fibres.[31] In humans[31]:
- most hypertrophy is due to fibre hypertrophy
- fibre hyperplasia may also contribute
- fibre hypertrophy versus fibre hyperplasia may depend on resistance training intensity / load
- higher intensity results in type II muscle fibre hypertrophy
- fibre hyperplasia may only occur in certain individuals under certain conditions
Neural Activation and Hypertrophy[edit | edit source]
Short-term increase in muscle strength | Long-term increase in muscle strength |
---|---|
Substantial increase in 1 repetition max (1RM) | Associated with significant fibre hypertrophy |
Due to an increase in voluntary neural activation | Net increase in protein synthesis takes time to occur |
Neural factors are critical in the first 8 to 10 weeks | Hypertrophy is the major factor after 8 -10 weeks |
Immobilisation and Muscle Strength[edit | edit source]
- Major changes occur after 6 hours of immobilisation:[32]
- lack of muscle use leads to reduced rate of protein synthesis
- initiates process of muscle atrophy
- During the first week: strength loss of 3-4% per day
- (Reversible) effects on types I and II fibres
- cross-sectional area decreases, cell contents degenerate
- type I fibres are affected more than type II fibres
References[edit | edit source]
- ↑ 1.0 1.1 Aspetar Clinical Guidelines: Safe return to sport during the Covid-19 pandemic version 2.0. 2021
- ↑ Soccer Physiologist. DETRAINING - What Happens When We Stop Exercising? Available from: https://www.youtube.com/watch?v=-dT5CC3LaV0 [last accessed 4/12/2022]
- ↑ Kasper K. Sports training principles. Current Sports Medicine Reports. 2019 Apr 1;18(4):95-6.
- ↑ 4.0 4.1 4.2 Physiopedia. Principles of Exercise
- ↑ Powers SK and Howley ET. Exercise Physiology: Theory and Application to Fitness and Performance.10th edition. North Ride, NSW, Australia. McGraw Hill. 2014
- ↑ 6.0 6.1 6.2 Maestroni L, Read P, Bishop C, Papadopoulos K, Suchomel TJ, Comfort P, Turner A. The benefits of strength training on musculoskeletal system health: practical applications for interdisciplinary care. Sports Medicine. 2020 Aug;50(8):1431-50.
- ↑ Suchomel TJ, Nimphius S, Bellon CR, Stone MH. The importance of muscular strength: training considerations. Sports medicine. 2018 Apr;48(4):765-85.
- ↑ 8.0 8.1 Dorrell HF, Smith MF, Gee TI. Comparison of velocity-based and traditional percentage-based loading methods on maximal strength and power adaptations. The Journal of Strength & Conditioning Research. 2020 Jan 1;34(1):46-53.
- ↑ Siddique U, Rahman S, Frazer AK, Pearce AJ, Howatson G, Kidgell DJ. Determining the sites of neural adaptations to resistance training: a systematic review and meta-analysis. Sports Medicine. 2020 Jun;50(6):1107-28.
- ↑ 10.0 10.1 10.2 10.3 Škarabot J, Brownstein CG, Casolo A, Del Vecchio A, Ansdell P. The knowns and unknowns of neural adaptations to resistance training. European Journal of Applied Physiology. 2021 Mar;121(3):675-85.
- ↑ Aagaard P, Simonsen E, Andersen J et al. Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses. J Appl Physiol. 2002;92: 2309-18.
- ↑ 12.0 12.1 Pucci AR, Griffin L, Cafarelli E. Maximal motor unit firing rates during isometric resistance training in men. Experimental physiology. 2006 Jan;91(1):171-8.
- ↑ Casolo A, Del Vecchio A, Balshaw TG, Maeo S, Lanza MB, Felici F, Folland JP, Farina D. Behavior of motor units during submaximal isometric contractions in chronically strength-trained individuals. Journal of Applied Physiology. 2021 Nov 1;131(5):1584-98.
- ↑ Walker S. Evidence of resistance training-induced neural adaptation in older adults. Experimental Gerontology. 2021 Aug 1;151:111408.
- ↑ Hakkinen K, Alen M, Kraemer WJ et al. Neuromuscular adaptations during concurrent strength and endurance training versus strength training. Eur J Appl Physio. 2003;89:42-52.
- ↑ Schoenfeld BJ. Is there a minimum intensity threshold for resistance training-induced hypertrophic adaptations?. Sports Medicine. 2013 Dec;43(12):1279-88.
- ↑ Morton RW, Colenso-Semple L, Phillips SM. Training for strength and hypertrophy: an evidence-based approach. Current Opinion in Physiology. 2019 Aug 1;10:90-5.
- ↑ Michael Wiggs. Hypertrophy vs Neural Adaptations. Available from: https://www.youtube.com/watch?v=pct0XWrWUfk [last accessed 5/12/2022]
- ↑ Carroll TJ, Riek S, Carson RG. Neural adaptations to resistance training. Sports medicine. 2001 Oct;31(12):829-40.
- ↑ 20.0 20.1 Maestroni L, Read P, Bishop C, Turner A. Strength and power training in rehabilitation: underpinning principles and practical strategies to return athletes to high performance. Sports Medicine. 2020 Feb;50(2):239-52.
- ↑ Enoka RM, Duchateau J. Rate coding and the control of muscle force. Cold Spring Harbor perspectives in medicine. 2017 Oct 1;7(10):a029702.
- ↑ 22.0 22.1 Chalmers G. Strength training: Do Golgi tendon organs really inhibit muscle activity at high force levels to save muscles from injury, and adapt with strength training?. Sports Biomechanics. 2002 Jul 1;1(2):239-49.
- ↑ 23.0 23.1 23.2 Kumar P, Singh D. Chapter-6 Strength Gains: Neuromuscular Adaptation to Resistance Training. Chief Editor Dr. Deba Prasad Sahu. 2019;95:95.
- ↑ Hryvniak D, Wilder RP, Jenkins J, Statuta SM. Therapeutic Exercise. In Braddom's Physical Medicine and Rehabilitation 2021 Jan 1 (pp. 291-315). Elsevier.
- ↑ Wilmore J, Costill D, Larry Kenney W. Physiology of Sport and Exercise: 3" Edition. Champaign, lL: Human Kinetics. 2005.
- ↑ Haun CT, Vann CG, Roberts BM, Vigotsky AD, Schoenfeld BJ, Roberts MD. A critical evaluation of the biological construct skeletal muscle hypertrophy: size matters but so does the measurement. Frontiers in physiology. 2019:247.
- ↑ Haun CT, Vann CG, Osburn SC, Mumford PW, Roberson PA, Romero MA, Fox CD, Johnson CA, Parry HA, Kavazis AN, Moon JR. Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy. PLoS One. 2019 Jun 5;14(6):e0215267.
- ↑ Abou Sawan S, Hodson N, Malowany JM, West DW, Tinline-Goodfellow C, Brook MS, Smith K, Atherton PJ, Kumbhare D, Moore DR. Trained Integrated Postexercise Myofibrillar Protein Synthesis Rates Correlate with Hypertrophy in Young Males and Females. Medicine & Science in Sports & Exercise. 2022 Jun 1;54(6):953-64.
- ↑ Damas F, Libardi CA, Ugrinowitsch C. The development of skeletal muscle hypertrophy through resistance training: the role of muscle damage and muscle protein synthesis. European journal of applied physiology. 2018 Mar;118(3):485-500.
- ↑ Horwath O, Apró W, Moberg M, Godhe M, Helge T, Ekblom M, Hirschberg AL, Ekblom B. Fiber type-specific hypertrophy and increased capillarization in skeletal muscle following testosterone administration in young women. Journal of applied physiology. 2020 May 1;128(5):1240-50.
- ↑ 31.0 31.1 Macdougall JD. Hypertrophy and hyperplasia. Strength and power in sport. 2003 Jan 1:252.
- ↑ Appell HJ. Muscular atrophy following immobilisation. Sports medicine. 1990 Jul;10(1):42-58.
- ↑ 33.0 33.1 Campbell M, Varley-Campbell J, Fulford J, Taylor B, Mileva KN, Bowtell JL. Effect of immobilisation on neuromuscular function in vivo in humans: a systematic review. Sports Medicine. 2019 Jun;49(6):931-50.