Is it normal for the muscle to increase as a result of resistance training Why?

Resistance Exercise Training to Shift mtDNA Genotype

The proportion of mutant mtDNA in muscle correlates with the degree of reduction in oxidative capacity. Recently there has been increasing interest in the role of exercise therapy to improve muscle respiratory chain oxidative capacity by potentially reducing mutant mtDNA load—a process known asgene shifting. Certain mtDNA mutations such as deletions and some tRNA point mutations are present in high levels in mature skeletal muscle, but for reasons that remain unclear, they are absent from the muscle satellite cell population, which harbors only wild-type mtDNA. Previous experimental work demonstrated that activation of satellite cells has the potential to introduce wild-type mtDNA into mature skeletal muscle, thereby lowering the proportion of mutant mtDNA and reversing the respiratory chain defect. Certain types of exercise protocols have the potential to induce satellite cell activation and promote entry of wild-type mtDNA into mature muscle. Endurance training has been demonstrated to improve aerobic capacity (Taivassalo et al., 2006) and OXPHOS capacity and exercise tolerance (Jeppesen et al., 2009) in patients with mitochondrial myopathy. A 12-week progressive overload leg resistance exercise training protocol has demonstrated increased muscle strength and improved muscle oxidative capacity, although there was no measurable reduction in deleted mtDNA (Murphy et al., 2008) and exercise has been accompanied by an increase in mutant mtDNA load in one study (Taivassalo et al., 2001).

Strength training for partially paralysed muscles

While a lot is known about strength training for non-paralysed muscles, the same cannot be said for training of partially paralysed muscles following spinal cord injury. There are few clinical trials in this area,73,76–79 and few involving patients with other neurological disabilities.18,80–94 Evidence about the carry-over effects of strength training on mobility are as yet inconclusive.18,94,95

It is generally assumed that the most effective way to increase strength in partially paralysed muscles is by adopting the same principles of progressive resistance training which are recommended for non-paralysed muscles. Exercises for muscles with grade 2/5 strength are done in gravity-eliminated positions. The easiest way to do this is to exercise in a horizontal plane. For example, the biceps muscles can be trained in side-lying with slings to support the arm (see Figure 8.6a). From this position patients flex the elbow horizontally through range. Similarly, patients with grade 2/5 strength in their hamstring muscles can flex the knee while lying on their sides with a slideboard between their legs (see Figure 8.6b). In these examples the only resistance to movement is provided by the passive properties of the joints and the friction of the slideboard. As soon as patients can move through range 8–12 times with gravity eliminated then patient position is changed and the limb is lifted against gravity. The resistance can be gradually increased by progressively rotating the plane of the movement away from the horizontal. Alternatively, it is possible to use specifically designed devices which enable strength training for the very weak in anti-gravity positions (see Figure 8.7). However, in practice it is difficult, with very weak muscles, to set the resistance to an 8–12 RM training load. The closest possible approximations need to be used.

Strength training for patients with partial paralysis can also be done within the context of motor tasks. For example, patients with partial paralysis of the lower limbs and difficulty standing can perform squats while standing on a sliding tilt table (see Figure 8.8). Resistance can be changed by adjusting the tilt of the table or adding weights to the sliding mechanism. In this way, most of the muscles responsible for upright standing are trained at the one time.

Maximal Resistance Training Increases Muscle Strength

One of the cardinal principles of muscle development during athletic training is the following: Muscles that function under no load, even if they are exercised for hours on end, increase little in strength. At the other extreme, muscles that contract at more than 50% maximal force of contraction will develop strength rapidly even if the contractions are performed only a few times each day. Using this principle, experiments on muscle building have shown thatsix nearly maximal muscle contractions performed in three sets 3 days a week give approximately optimal increase in muscle strength without producing chronic muscle fatigue.

The upper curve inFigure 85-6 shows the approximate percentage increase in strength that can be achieved in a previously untrained young person by this resistive training program, demonstrating that the muscle strength increases about 30% during the first 6 to 8 weeks but almost plateaus after that time. Along with this increase in strength is an approximately equal percentage increase in muscle mass, which is calledmuscle hypertrophy.

In old age, many people become so sedentary that their muscles atrophy tremendously. In these cases, however, muscle training may increase muscle strength more than 100%.

Hypertrophy

One of the most prominent adaptations to strength training is muscle enlargement. The growth in muscle size is primarily due to an increase in the size of the individual muscle fibre (Fleck and Kraemer, 2004). According to Fleck and Kraemer (2004), humans have a potential to hyperplasia, but it does not happen on a large scale and is far from the dominating cause of hypertrophy. An increase in the number of muscle fibres has been shown in birds and mammals, but there are limited data to prove this in humans.

The increase in cross-sectional area is attributed to increased size and number of the contractile proteins (actin and myosin filaments) and the addition of sarcomeres within existing muscle fibres. An increase in non-contractile proteins has also been suggested.

Satellite cells and myonuclei may indicate cellular repair after training and the formation of new muscle cells, and the proportion of satellite cells that appear morphologically active, increase as a result of resistance training (Fleck and Kraemer, 2004).

Muscle fibre hypertrophy has been found in both type I and type II fibres after strength training. However, most studies show greater hypertrophy in type II and especially IIa fibres (Kraemer et al., 1995; Green et al., 1999). Genetic factors decide whether a person has predominantly type I or type II muscle fibres, and though transitions from type IIb (now named IIx) to type IIa have been found (Adams et al., 1993; Green et al., 1999; Campos et al., 2002), such changes only seem to happen within fibre type (e.g. not from type II to type I; Fleck and Kraemer, 2004). Cessation of training leads to transitions back from IIa to IIb. But even if most studies fail to find changes in the amount of type I fibres, some strength and sprint studies do. Kadi and Thornell (1999) found that there was a significant increase in the amount of MyHC IIa protein and a significant decrease of the amount of MyHC I and IIb in the trapezius muscle of women in the strength group.

Different muscles have different distributions of fibre types and the total number of muscle fibres varies between individuals. Because the number and distribution of muscle fibres does not seem to be the dominant factor for hypertrophy, and it is impossible to evaluate the number and distribution of muscle fibres in an individual without biopsies, types of muscle fibres should be disregarded as a factor when prescribing PFMT. The aim is to target as many motor units as possible in each contraction.

Greater hypertrophy has been associated with high-volume compared to low-volume programmes (Kraemer and Ratamess, 2004). Short rest intervals have also been shown to be beneficial for hypertrophy and local muscle endurance (Kraemer and Ratamess, 2004). Some studies suggest that a fatigue stimulus with metabolic stress factors has an influence on optimal strength development and muscle growth, even if the mechanisms are unknown. Rooney et al. (1994) found that a 30-second rest between each lift gave a significant lower strength increase than the same amount of repetitions and loads with no rest between the lifts. Maximal hypertrophy may be best attained by a combination of strength and hypertrophy training. One study showed greater increases in cross-sectional area and strength when training was divided into two sessions a day rather than one (Kraemer and Ratamess, 2004).

With the initiation of a strength training regimen, changes in the types of muscle proteins start to take place within a couple of workouts. This is caused by increased protein synthesis, a decrease in protein degradation, or a combination of both. Protein synthesis is significantly elevated up to 48 hours after exercise (Fleck and Kraemer, 2004). However, to demonstrate significant muscle fibre hypertrophy, a longer training time is required (> 8 weeks) (Fleck and Kraemer, 2004). As studies are demonstrating an elevated muscle protein synthesis after an acute strength training bout (Biolo et al., 1995; MacDougall et al., 1995; Phillips et al., 1997), the discrepancy seen between increased strength and muscle growth early in a strength training regimen may be more due to methodological problems in measuring small changes in muscle cross-sectional area rather than the traditionally assumed effect of neural adaptation. Another contributing factor that can explain why the role of neural adaptation may be overestimated at the beginning of a strength training programme is an increase of muscle fibre girth at the expense of extracellular spaces (Åstrand et al., 2003). In most training studies increase in muscle fibre cross-sectional area ranges from about 20% to 40% (Fleck and Kraemer, 2004). In an uncontrolled PFMT trial Bernstein (1996) found an increase in levator ani thickness of 7.6% at rest and 9.3% during contraction, while the increase in PFM thickness was 15.6% in the randomized controlled trial by Brækken et al. (2010). Is a voluntary PFM contraction a concentric or isometric muscle action? MRI studies (Bø et al., 2001) have shown that there is a movement of the coccyx during PFM contraction. Hence, the contraction is concentric. However, this movement is small and there therefore must be an isometric component of PFMT. It has been suggested that 6 s is necessary to reach maximum contraction. However, holding times between 3 and 10 s are recommended for isometric contractions (Fleck and Kraemer, 2004). Daily isometric training is superior to less frequent training, but three training sessions per week will bring significant increases in maximal strength. Isometric training alone with no external weights has been shown to increase protein synthesis 49% and muscular hypertrophy of both type I and type II muscle fibres. Twelve weeks of training increased knee extensor cross-sectional area 8% and muscle isometric strength 41% (Fleck and Kraemer, 2004). PFM action is eccentric during increases in abdominal pressure.

Resistance Training and Rehabilitation

Resistance training (also referred to as strength training) is a progressive use of varying loads, movements, and velocities to improve muscle strength power, and endurance.62 To prevent injury in the young dancer, it can be beneficial to incorporate strength and integrative resistance training, as well as flexibility work.13 There is a new shift from post injury rehabilitation to injury prevention using resistance training. However, many dancers are hesitant to participate in resistance training with the fear that it will increase muscle bulk, while taking away from ballet aesthetic. Integrating resistance training into dance training will help improve core stability and lower extremity strength, without dramatic increase in muscle bulk or change in aesthetics.62

It is important to understand that resistance training in children is safe and will not negatively impact growth or be injurious to immature skeletons, as long as conducted with a qualified instructor who monitors technique and progression. Finally, most young dancers should participate in resistance training as an integral part of their routine dance training. Although dancers have been found to have strong lower extremities, supplemental resistance training can improve both muscular and anaerobic power, as well as serve to prevent future injury. There is a need in the dance community to dispel the myths surrounding resistance training and to continue to be informed of the significant benefits, effectiveness, and safety of strength and resistance training.

Resistance Exercise

Resistance training is primarily designed to improve muscle fitness by exercising a muscle or a muscle group against external resistance (such as free weights, weight machines, body weight, elastic tubing, medicine balls, or even common household products). The caveat with resistance exercise is that it is important to ensure maintenance of correct technique to minimize injury, which, for most nonexercising individuals, requires proper tuition and supervision. Guidelines for undertaking resistance exercise differ depending on whether hypertrophy, muscular strength, power, and endurance are the targeted outcomes.4 Resistance exercise should form an important part of any exercise training program because it is associated with many exercise-specific health benefits, such as the prevention of sarcopenia and preservation of bone mineral density, both of which are associated with aging and inactivity.22,23 However, resistance exercise is often overlooked from a weight management perspective. Overall, little evidence exists, demonstrating that resistance exercise training alone promotes weight loss. In one study conducted by Church and colleagues,24 9 months of resistance exercise training did not result in a significant change in weight compared with a nonexercise control group, and this seems to be a consistent finding within the literature.14,25 Although resistance exercise may not improve weight loss per se, resistance training does contribute to the reduction of body fat7 and increases lean body mass.26 Thus, people with obesity performing resistance exercise may not see significant reductions in weight, whereas they can expect improvements in body composition.

Exercise

Resistance exercise has an established influence on muscle strengthening and muscle protein synthesis. The beneficial effects of resistance training have been well documented in healthy adults, adolescents, and older children.22–26 Ferrando et al. demonstrated in healthy adults that moderate resistance exercise is capable of ameliorating the decreases in skeletal muscle protein synthesis and strength that accompany inactivity.27 The acute stimulatory effects of resistance exercise may last up to 48 hours.28 In burns, resistance exercise alone is also capable of inducing increases in lean mass and muscle strength. Suman et al. demonstrated in severely burned children and adolescents that a 12-week exercise program of resistive and aerobic exercise significantly improved lean mass and muscle strength relative to standard of care treatment (Figure 51.3).29

Expansion of the Skeletal Muscle Microvascular Network

RT also leads to an increase in skeletal muscle vascularization. Since repeated resistance exercises increase the mean fiber cross-sectional area, expansion of the microvascular network is required to ensure the delivery of oxygen and amino acids required for muscle growth. An increase in the capillary-to-fiber ratio is commonly reported following prolonged RT [47], and this adaptive response contributes to maintain, but not increase, perfusion capacity, oxygen, and substrate delivery. A recent study clearly demonstrated that myofiber hypertrophy and increased capillarization occurred in tandem during RT [48]. Because the amino acid availability within myofibers is required for protein synthesis, it could be speculated that angiogenesis develops during RT likely to preserve the oxygen and substrate diffusion capacity, and then muscle hypertrophy may be facilitated by the expansion of the muscle microvasculature.

Musculoskeletal Disorders

Resistance exercise, like other forms of exercise, has been shown to cause decreased pain perception in humans shortly after exercise has been completed (Galdino et al., 2014). Most other studies have shown hypoalgesia as a result of high-intensity exercise like running and cycling, but pain perception using pressure stimuli was also influenced by resistance exercise (Galdino et al., 2014). The hypoalgesic effect of resistance exercise may be of significant importance for individuals suffering from musculoskeletal disorders like osteoarthritis (Galdino et al., 2014). Musculoskeletal disorders are most often associated with both muscular atrophy and pain. Resistance exercise may prove to be important in managing these symptoms partially due to the endocannabinoid system’s role in hypoalgesia (Galdino et al., 2014). The effectiveness of resistance exercise to treat certain musculoskeletal disorders has already been proven based on the theory that strengthening various muscles allows for greater function (Galdino et al., 2014). The ability of resistance exercise to cause pain reduction partially due to the endocannabinoid system has also been experimentally proven (Galdino et al., 2014). Resistance exercise seems to be an even more effective treatment for musculoskeletal disorders when considering both the effects it has on managing pain and improving motor function.

The Role of Exercise in the Management of Type 2 Diabetes

Exercise has long been considered an essential part of therapeutic lifestyle modification in diabetes management. However, evidence from controlled studies only has become available in recent years. Results from intervention trials showed that the beneficial effect of exercise on glycemic control is independent of weight loss. Increased exercise intensity also appears to be associated with further reduction in HbA1c (an indicator for the average amount of blood glucose over a period of time). Exercise can also improve cardiovascular outcome in type 2 diabetes. A structured exercise program can be planned to achieve specific fitness and health goals by involving different types of exercise. Types of exercise that have been evaluated for diabetes management include aerobic exercise and resistance training. Aerobic exercise refers to the phase in exercise when oxygen is used to burn glucose and fat to generate energy for muscle cells. Aerobic exercise can be any exercise; it generally requires the exercise to be performed at a moderate intensity over a long period of time to get past the initial anaerobic phase. As a general guideline, the American Diabetes Association recommends at least 150 min/week of moderate-intensity aerobic physical activity and/or at least 90 min/week of vigorous aerobic exercise to improve glycemic control, assist with weight maintenance, and reduce the risk of cardiovascular complications. The exercise should be distributed over at least 3 days/week, with no more than 2 consecutive days without physical activity. The amount of exercise can be adjusted to meet different goals. For example, increasing the amount and intensity may be helpful in further cardiovascular disease risk reduction and in long-term weight maintenance.

Resistance training aims to develop and enhance muscle strength. This type of exercise is performed against a specific opposing force, for example, weights, resistance bands, or, in some exercises, human body weight. The value of resistance training in diabetes management has been proven in randomized controlled studies. For patients for whom aerobic exercise may be contraindicated, such as patients with advanced peripheral neuropathy, or severely obese patients for whom performing aerobic exercise is physically challenging, resistance training may be a desirable alternative. By increasing muscle mass and endurance, resistance training can often result in more rapid changes in functional status and body composition, and therefore may be more rewarding and encouraging for patients. It is shown that resistance exercise improves insulin resistance to similar extent as aerobic exercise. As a general guideline, the ADA recommends:

type 2 diabetic patients (those who do not have contraindications) perform resistance exercise three times week, targeting all major muscle groups, progressing to three sets of 8–10 repetitions at a weight that cannot be lifted more than 8–10 times(Sigal et al., 2006).

To ensure resistance exercises are performed correctly, to maximize health benefits, and to minimize the risk of injury, initial supervision and periodic reassessments by a qualified exercise specialist are recommended.

A complete physical examination and exercise stress test should be performed before beginning an exercise program for certain patients. The patient's age, previous physical activity level, and medical history should be considered. Exercise stress tests using electrocardiograms (ECG) should be considered for previously sedentary patients at moderate or high risk of cardiovascular disease who want to undertake vigorous aerobic exercise exceeding the demands of everyday living.