Human Physiology: The Sliding Filament Theory

An experiment was conducted to look at the relationship between grip strength and blood pressure. This relationship was inspected by the conduction of several experiments on several different volunteers that varied in factors such as, age, weight and muscle mass. The experiment aimed to assess grip strength and also fatigue that formed due to excessive muscle contraction. The way, in which muscle contraction occurs, is due to the stimulation of those muscle fibres. This stimulation develops due to action potentials. 

‘The sliding filament theory is an explanation for how muscles contract to produce force’. Therefore the theory allows scientists to comprehend muscle contraction and its molecular basis.' When an action potential reaches the sarcoplasmic reticulum it stimulates the opening of calcium ion channels. The calcium ions then diffuse down a concentration gradient, flooding the sarcoplasm with calcium ions’ (Fisher, 2017,p376). Now, on the actin filament, tropomyosin and troponin prevent myosin from binding to actin. Here the calcium ions play a role in binding to troponin, causing its shape to change. This change pulls the tropomyosin away from the actin-myosin binding site, allowing the myosin head to bind to the actin filament. The energy provided by the hydrolysis of ATP maneuvers the cycle of this muscle contraction.

Repeated muscle contraction, helps maintain homeostasis within the body, due to the regulation of heat. Heat production is usually a by-product of muscular metabolism, and this production is particularly evident during exercise, as exercise promotes muscle contraction and therefore increases body temperature. ‘Physical training alters the appearance of skeletal muscles and can produce changes in muscle performance. Conversely, a lack of use can result in decreased performance and muscle appearance’. These changes usually occur due to Hypertrophy- an increase in muscular size, which are accommodated with additional changes to the cellular components of the muscle. 

An increase in muscle mass provides the strength required for posture and mobility, which fundamentally improves the physical health of an individual. Typically with exercise, blood pressure increases-specifically systolic blood pressure (a measure of blood vessel pressure when your heart beats) but it should gradually return back to normal, after exercising. Additionally, grip strength is said to also increase due to exercise as continual muscle contraction strengthens a persons grip and the muscles that are being trained, therefore grip strength fatigue is less likely to occur as result. 

The association between Grip strength and total body mass (BMI) is prominent in numerous amount of studies. The assessment of these two factors has been used effectively to determine the quality of muscle mass and can also be used to predict the likelihood of someone suffering from a form of cognitive impairment. ‘Handgrip strength (a form of isometric static contraction test) is an important test to evaluate the physical and nutritional status of an individual’.

Record the participant’s height (cm) using a stadiometer, their weight (kg) using weighing scales and percentage body fat (%BF). Measure there (%BF) by using the Omron handheld device. The participant should turn the device on. Press ‘set’ using the arrow keys to set height, then press 'set' again to confirm. Continue, inputting the weight, age, and gender of your participant. Press start and then grip the device in both hands. Record the subsequent BF%. Measure the blood pressure of the participant while they are seated in a chair. Make sure the participant is relaxed and comfortable, with their arm being used for measurement resting comfortably on a table approximately level with the participant’s heart. 

Next, place the blood pressure cuff above the elbow underneath the participant's clothing. If the cuff has an arrow or artery marker, this should be placed directly on top of the brachial artery (slightly middle of the midline of the anterior of the arm). Ask the participant to keep still and to avoid talking while the blood pressure measurement is being taken. This procedure was done to gather accurate readings.

Here the graph shows that as the fat-free mass increases the maximal grip strength also increases. Here there is a positive correlation between the two factors and the line of best-fit displays this. There are a few outliers at around 30-52(kg) of fat-free mass with a generation of 70-77(kg) of the maximal grip strength. These anomalies deviate from the common trend that the graph shows, meaning that they could have been caused by an inaccurate collection of the results.

Aim 1 stated –‘Examine the feasibility of using a large cohort of investigators to collect data for a force fatigue curve’. Evidently, in figure 1 there is not a prominent curve formed however; there is some sort of correlation between time and the average grip strength. The graph depicts the exponential decrease in average grip strength, as time increases. Therefore during the practical, the participant’s levels of fatigue increased. This increase may have been due to the continuous use of the same muscle fibres-possibly causing the production of lactic acid (anaerobically). This production occurs through the conversion of pyruvate to lactate. The accumulation of high levels of lactate increases the acidity in the muscle cells hence ‘the same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment.’ 

Fatigue may have also been generated by other factors such as varying body fat percentages within participants Depending on an individuals body composition, the effect that fat may have on muscle performance differs. Obesity, for example, creates many functional limitations on muscles, causing mobility difficulties within an individual, even though ‘the general consensus is that obese individuals. Have a greater absolute maximum muscle strength’ in comparison to someone who isn’t obese. This increase in adipose tissue ‘acts as a chronic overload stimulus’ on the ‘antigravity muscles, thus, increasing muscle size and strength’ yet, these individuals seem weaker (muscle mobility is slower). 

A study was conducted in order to access grip strength and its association within 200 patients varying from around 20-88 years. The results produced were fairly similar to the results generated in this study as both showed a correlation between the grip strength and time producing a downward fatigue curve. Besides this figure 1 also has very large error bars. The errors bars suggest that data generated may not be reliable and seeing as the error bars overlap the data may not be as significantly significant.

Aim 2 stated- “Establish the effect of this grip strength protocol on the blood pressure response.' The association between the blood pressure and handgrip strength is apparent not only within this study but in numerous amounts of other studies. In this study, figure 2 displays that before the handgrip exercise the systolic (118.3) and diastolic (75.2) pressure were both higher than the values gathered after the handgrip procedure-Systolic (117.09) and Diastolic (74.04). Even though the reduction may not be significant it is still of value to researchers. 

Systolic blood pressure is the force at which blood pushes against the arterial walls in the heart, while the ventricles squeeze blood out so that it is transported to the rest of the body. Diastolic blood pressure measures the force of blood against the arterial walls while the ventricles relax and refill with blood. Diastole is the period at which ‘the heart relaxes between beats.’ Typically, after full-body exercise, blood pressure increases. This is the result of countless amounts of activities (specifically aerobic) that ‘put additional demands on the cardiovascular system.’ 

Fundamentally, the body’s requirements are to sustain sufficient amounts of oxygen via the blood cells to the muscles. Therefore increased breathing and heart rate are needed for the body to establish protocol. The handgrip experiment is isometric, meaning that only a specific area of the body was ‘exercised’. A Meta-analysis study was conducted to access the effects that endurance training had on blood pressure, and also hypertension. The results from that study concluded that ‘aerobic endurance training decreases blood pressure through a reduction of vascular resistance’. Essentially, this trend was also apparent within the isometric handgrip protocol that was conducted suggesting that blood pressure decreases after general exercise.

Aim 3 stated-“ Examine the association between maximal grip strength and fat-free mass in kg.' based on the aim there was an expectation that there would be a relationship between maximal grip strength and maximal grip strength. Primarily, the graph depicts this association, showing that as the fat-free mass (kg) increases the maximal grip strength also increases. Therefore we can form a prediction by using the graph that supposedly the higher the amount of fat-free mass that someone has the higher there maximal grip strength value. The line of best fit indicates an exponential growth of the maximal grips strength and can also be used to predict maximal grip strength values, meaning that the data is very accessible. 'Fat-free mass is a phrase used to describe all of the tissues in the body that are not adipose tissue’. 'Fat-free mass includes most of your body’s vital organs and cells’ including, organs, muscle, bone connective tissue and water. Increased fat-free mass has its benefits; including improving metabolism and daily movement-as the muscles are stronger and much more flexible.

In conclusion, the experiment was successful. The procedure ran smoothly and the data and results were produced with ease. One way in which the experiment could be improved is by generating a different cohort of individuals ranging in similar age, fat-free mass and body composition. This generation could be done through questionnaires and also health checks to verify if a participant is fit enough to take part in the practical. This would, therefore, reduce the strain of confounding variables as these variables usually produce a ‘hidden effect on experimental outcomes’.

Age was on a variable that researchers have no control over but did have a direct effect on the experiment. As mentioned this effect can be minimized by the use of volunteer sampling to deduce expectations from the self-selected participants. Another factor could be human error. Miscalculation of blood pressure of weight could easily have affected the accuracy of the results and also its reliability. Generally, average grip strength decreases over time, additional to blood pressure and fat-free mass.