Strength

Strength

Overlooked Factors Thank Influence Muscular Strength

Muscular fitness consists of three factors: endurance, power, and strength.  Muscular endurance is the muscle’s ability to resist repeated contractions and/or maintain a contraction over a period of time [1]. Muscular power, also called explosive strength, is the ability of the muscle to maximally contract in a short period of time [1]. Lastly, muscular strength is the ability to generate force or torque [1]. Full body and compound strength training implemented within a strength and conditioning program has the capacity to enhance each component of muscular fitness. Specifically, in regards to muscular strength, whether strengthening specific joints like the knee, lower-back, or core, muscular strength (for beginners or athletes) enhances both general and sport specific athletic performance while simultaneously reducing the risk of injury [2,3,4]. Collectively, the greater muscular endurance, power, and strength, the greater muscular fitness someone has. 


Enhancing muscular fitness through strength training is being recognized in the pathogenesis and prevention of many chronic diseases that plague society [5,6]. Muscular fitness has become such an important part of fitness that muscle strengthening activities are currently in most institutional and governmental guidelines of exercise to maintain overall health [7,8]. Enhanced muscular strength and fitness has previously demonstrated an inverse relationship between cardiovascular disease as well as metabolic risk factors and has even demonstrated a positive association to bone health and self-esteem [9]. In essence, a lack of strength may ultimately lead to disease and decreased quality of life. 


Optimizing strength in muscles looks different for everyone and not everyone may be able to or want to participate in strength training. This is where PowerDot Smart Neuromuscular Electrical Stimulation (NMES) technology comes in as it’s an FDA approved device that is safe to use for all populations ranging from clinical to athletic populations. For healthy and athletic individuals, adding PowerDot NMES to physical training has the capacity to further enhance strength and muscular adaptations [10,11]. In clinical populations, NMES training lowers the burden of respiratory stress during exercise and enhances muscular strength in patients with minimal capacities for exercise, like those with Chronic Obstructive Pulmonary Disease (COPD) [12]. However, understanding how to enhance muscular strength is just one aspect, the community should be aware that there are several other factors that ultimately impact the muscle’s ability to generate force. 


Strength training and using NMES technology is the most optimal means of enhancing muscular force production (ie. strength). Though, there are a total of six factors that influence the development and maintenance of muscular strength. The first factor is genetics. Genetics plays a role as some have DNA that make them genetically stronger than others [13]. The second factor is nervous system activation. Muscular force production and strength is dependent on the nervous systems ability to quickly signal and cause muscle fibers to contract [14]. The third factor is general physical activity. Just participating in general physical activity and not just resistance training positively impacts strength [15]. The fourth factor is nutritional activity. Specifically, protein and amino acids are able to stimulate a muscle building pathway that leads to increases in strength [16,17]. The fifth factor is dependent on the endocrine system. Hormones play a key role in promoting muscle protein synthesis ultimately enhancing muscle mass and strength [18]. Lastly, the sixth factor is environmental. Who and what people are surrounded by has a major impact on muscular strength and fitness [19]. Strength is influenced by many uncontrollable factors and it’s important to utilize the highest standard of NMES technology, innovated by PowerDot, to further enhance strength adaptations through factors that can be controlled


Genetic Determinants of Muscular Strength

“They just have good genetics” is a common saying. But what does that really mean? To explore genetics and its implications in enhanced muscular force production, it’s important to know a little more about the study of genetics… then it will be clear how genetics is implicated in muscular force/strength production.


Every cell in the human body, yes even muscle cells (muscle cells = muscle fibers), have a nucleus with forty-six chromosomes. Chromosomes are structures within the cell's nucleus that contains a person's genes. Genes are composed of a sequence of genetic material, called DNA. This sequence of DNA is what leads to the outward characteristics and traits we display (phenotypes)… ie. hair color and strength. These genes may have several different sequences making them polymorphic. For instance, the genes that control hair color are polymorphic as there are several different sequences that lead to various hair colors. Scientists have discovered that there are several genetic polymorphisms that contribute to strength [20]. 


Muscular strength has a heritability component to it. Focusing on strength, heritability is the differences in the appearance of a trait (strength) across several people due to differences in their genes. When examining twins, whose genetic DNA would be similar, it has actually been found that the heritability of muscle strength ranges from approximately 30 to 80% in various strength phenotypes such as isometric knee strength, handgrip strength, and elbow flexion [21,22,23,24]. Scientists have discovered over 200 genetic variants to be associated with health and fitness related phenotypes with 22 common genetic polymorphisms associated with muscular strength and power phenotypes [13,20]. In summary, there are numerous sequences of human genes (genetic polymorphisms) that contribute to components of physical fitness (phenotypes), like strength. 


Neural Drive and Muscular Force Production

Muscle quality and performance are enhanced via neural mechanisms by which an individual may increase force production by increasing motor unit (MU) activation, MU firing rate, MU synchronicity, and increasing agonist activation while decreasing antagonist activation [14,25,26,27]. Let’s rewind real quick and break this down. First, in order for a muscle to contract, there is an electrical signal that is sent from the brain/spinal cord to skeletal muscles resulting in muscular contraction. A motor unit (MU) is a single alpha-motor neuron and all of the muscle fibers that it innervates. The alpha-motor neuron is located in the spinal cord and sends an electrical signal to the muscle. Now, if more motor units are activated (increased MU activation), then more muscle fibers will be activated and contracting, enhancing force output. By increasing the firing rate of the motor unit, that electrical signal is being sent faster to the muscle. Typically, motor units fire asynchronously (not together) to reduce fatigue and allow for a smooth contraction. By increasing motor unit synchronicity, more motor units fire together and now more muscle fibers are contracting at the same time, enhancing force production. Lastly, antagonist muscles are muscles that oppose movement. Like, when doing a biceps curl, the triceps are the antagonists. If they are active then they will resist the biceps curl or make it harder to complete. By decreasing antagonist activation via reciprocal inhibition, the main prime mover muscle is now able to contract without opposition producing more force. A combination of these neural adaptations enhance muscular force production without any change at the muscle level.

 

Neural adaptations are a result of strength training and typically can be seen within weeks of starting a strength training program. This is why many may see huge improvements in strength within, say 4-weeks, and it is because of the neural adaptations described above. To demonstrate just how strong (no pun intended) the neural component of strength and force production is, let’s examine the concept of “cross-education”. Cross-education describes a phenomenon where unilateral training results in contralateral (other side or other limb) strength improvements [28]. Meaning, by doing a biceps curl with the right arm, the left arm will get stronger without performing any repetitions. This is due to neural adaptations and participants have demonstrated strength improvements of 8-9.5% in strength of the unused limb during unilateral training [28]. 

 

Physical Activity and/or Resistance Training Increases Strength

As previously mentioned, resistance strength training (lifting weights) increases muscular size and strength [29,30]. However, regular physical activity and recreation has also demonstrated the ability to not only enhance muscular strength, but also improve balance and endurance performance [31]. Meaning, there is no need to be a gym rat to increase muscular strength. General physical activity has the capability to increase strength and enhance functional limitations [15]. 

 

Skeletal muscle adaptations that increase muscular strength include: muscle hypertrophy (whole muscle growth), type II fiber hypertrophy (specific muscle fiber type growth), and it is hypothesized that myofilament packing may also aid in force development [32]. Myofilament packing suggests that there are more contractile muscle proteins in the muscle cells… and if there are more muscle contractile proteins, it means more force production. However, muscular strength is a dose dependent response. Meaning, the greater the muscular intensity (the higher the dose), the greater the improvements in strength (the greater the response) making strength training the more optimal form of exercise. 

 

Think of the SAID principle, which stands for Specific Adaptations to Imposed Demands… lifting something heavy and having to produce a lot of muscular force will result in muscles adapting to produce more force. To demonstrate this, heavy resistance training was compared to blood flow restriction training [2,33]. It’s important to note that blood flow restriction training is performed at lighter intensities. Though blood flow restriction training still increased muscle mass and strength, heavy resistance training promoted greater improvements in strength [2,33]. The takeaway, to get stronger (adaptation), heavy things should be lifted (imposed demand), though, general physical activity should not be overlooked. 

 

Nutritional Activity Cellular Signaling to Increase Muscular Strength 

Proper nutrition is emphasized to live a healthy lifestyle, cause weight loss, and help improve overall body composition. Poor nutrition and malnutrition negatively impact muscular strength [34]. Key nutritional factors to take into consideration are the three primary macronutrients the body metabolizes: carbohydrates, fats, and proteins. Carbohydrates and fats are the two primary food sources the human body uses to create energy in the form of ATP, which is needed to cause skeletal muscle contraction (important for muscular force production). However, in regards to enhancing muscle quality and its ability to produce force, it is essential to focus on protein/amino acid intake (amino acids are the building blocks of protein). 

 

Protein is essential for building muscle mass and strength. Ingestion of branched chain amino acids as well as whey protein supplementation provide an ergogenic (intended to enhance human performance) that enhances the acquisition of strength beyond what is achieved by just resistance training alone or resistance training and carbohydrate supplementation [16,35]. Ingestion of whey protein or an amino acid blend that specifically has higher contents of leucine (an essential amino acid) activates a cellular signaling pathway (mTOR) that stimulates muscle protein synthesis and cell growth resulting in bigger and stronger muscles [17].

 

A big controversy surrounding this topic is the timing of protein to promote optimal muscular improvements. It has been proposed that protein timing should be around the time of an exercise training session, however this theory has been refuted [36]. Just consuming adequate amounts of protein in combination with resistance training is the key to maximizing muscular adaptations [36]. 

 

Endocrine (Hormone) Influences on Muscular Force Production

When discussing the influences hormones have on muscular force production it is important to discuss the differences between endogenous and exogenous hormones. Endogenous hormones are the hormones that naturally circulate in the body. Exogenous hormones are from an outside source, for instance, taking steroids (testosterone, as it’s a steroid hormone). The evidence is very clear that exogenous anabolic hormone supplementation enhances muscular strength [37]. Just taking testosterone (that means not exercising or resistance training) has the ability to increase muscular strength more so than performing resistance training and not take testosterone [37]. However, we are interested in how endogenous hormone levels impact muscle quality and strength and this may be attributable to the specific design of a resistance training program. 

 

Up to now, it’s evident that resistance training is something that should be added into daily habits if aiming to maximize muscular force production. Hormonally, testosterone levels increase during heavy load or high-intensity exercise, however this is significantly greater in males in comparison to females [38]. However, the order of exercises in that training program may be just as important as it may impact hormonal concentrations [38]. More and more research is coming out suggesting that exercise order (exercising large muscles then small muscles), maximal intensity to failure with high volume, and minimal rest periods influences strength and hypertrophy [39]. This is supported in another study where participants performed leg exercises prior to arm exercises and demonstrated greater levels of serum testosterone and growth hormone leading to superior strength training adaptations [18]. By working from large muscles to small muscles and resistance training at a high intensity, greater anabolic hormone production may greatly impact muscular strength.

 

Environmental Impact on Muscular Force Production

There’s a quote saying, “show me your friends and I’ll show you your future”. The environment and surroundings significantly impact muscular fitness and strength as humans are products of their environment. 

 

The average person spends approximately 8 hours per day in personal screen time. That’s screentime outside of work! It’s to no surprise then that less than 5% of adults actually participate in physical activity each day and only 1 in 3 adults receive the recommended amount of physical activity each week (only 30 minutes of walking 5 days per week is what’s recommended) [40,41]. This is a devastating trend that is continuing to increase. It may be because the ability to be physically active is limited with only 1 in 5 homes having parks and/or fitness and recreation centers within a half-mile [42]. Also, only 6 states (Illinois, Hawaii, Massachusetts, Mississippi, New York and Vermont) require physical education in every grade (K-12) and those that are active at an early age remain more physically active across a lifespan [43,44]. It’s important for an environment to be conducive to promoting physical activity.

 

Not only does the community need an environment that promotes physical activity but one that supports nutritious habits. The typical American diet exceeds the recommended intake levels for the following: calories from solid fats and added sugars; refined grains; sodium; and saturated fat [40]. As previously mentioned, engaging in physical activity and proper nutrition positively impacts muscular strength. This demonstrates the negative impact an environment may have on either promoting or hindering muscular strength. 

 

Greater Improvements in Strength with NMES

PowerDot is an innovator in the NMES space. With the first FDA approved app-based NMES unit, PowerDot provides the highest standard of performance. Utilizing bluetooth technology, limiting wires and clunky devices, PowerDot NMES technology is controlled through an app on a phone or tablet. With several preset programs, PowerDot takes out the guesswork when it comes to enhancing muscular strength. The PowerDot NMES technology increases strength more than training without it as it further enhances neural drive through positive adaptations of the central nervous system and upregulates key anabolic muscular signaling pathways [45,46].  


For instance, by stimulating one leg with NMES and using the other leg as a control, scientists revealed a 24% increase in strength in the NMES leg and only a 10% increase in the control leg [47]. A case study examining an elite weightlifter found that in just two weeks of adding NMES, the athlete’s squat increased by 20 kg [11]. NMES in clinical populations has also demonstrated to be an effective treatment for improving muscle strength and function. In ACL reconstruction patients, those who were treated with NMES demonstrated greater quadriceps strength and returned to agility training sooner [10]. Lastly, NMES prior to surgery (knee replacement surgery), in those with osteoarthritis, demonstrated faster recovery of quadriceps muscle strength and a more expedited return to activity [48]. PowerDot Smart NMES technology was designed to be used by everyone so that all can experience the benefits of enhance muscular strength and fitness.



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