Effect of Maximal Grip Strength on Force Output and Blood Pressure

The following experiment is one that involves the repeated contraction of muscles in the forearm in order to obtain data of the maximal grip strength and the factors that affect it. Muscles are a type of connective tissue that are attached to the bone by tendons and to each other by ligaments, and the tissue responsible for movement. The muscles that this experiment is focusing on are the muscles in the forearm which is mainly made up of skeletal muscles. Skeletal muscles ordinarily have an extensive blood supply as muscles typically have an intricate system of capillaries that transport blood from a few larger veins or possibly a central artery. In addition, skeletal muscles are able to generate movement through 2 main mechanisms, the mechanical and the electrical that work together in order for contraction and relaxation to occur. The nervous system is generally responsible for the skeletal muscle’s voluntary movement according to. The type of muscle contractions taking place in this experiment is known as isometric contraction, which occurs when the length of the muscle remains the same and there is a force generated (tension that increases) in the muscle without placing any strain on the joints.

Skeletal muscles are mainly composed of many muscle fibres that are long and round, known as fascicles. These fascicles are then sub composed of many muscle fibre cells made up of myofibrils and a cellular membrane known as the sarcolemma as well as many organelles mainly mitochondria that are needed to produce ATP for movement of the muscle. Each muscle is connected to its own somatic nerves as well as its own specific artery and vein to supply blood and oxygen to the muscle. The myofilaments contain sections called sarcomeres that are made up of 2 main proteins, namely actin and myosin. During relaxation the actin and myosin myofilaments do not touch. This is due to the Actin being blocked by tropomyosin and troponin. When the brain sends an action potential to the motor neuron that’s connected to the muscle cell the receptors which are sodium channels open thus flooding the cell with sodium creating a gradient. Stored calcium ions from the sarcoplasmic reticulum is released into the cell via protein pumps and ATP is released from the mitochondria. The calcium ions bind to the troponin which then pulls the tropomyosin away from the actin sites. The myosin breaks down the ATP into ADP and Pi (a singular phosphate) and causing it to stretch. It then attaches to the actin and pulls it slightly causing the ADP and Pi to be released and allowing an ATP molecule to bind to the myosin thus releasing the myosin from the actin. This cycle of repeated muscle contraction is known as the sliding filament model.

During full body exercise blood pressure generally increases. This is because during exercise there is an increase in the amount of carbon dioxide in the blood which are detected by chemoreceptors, which send signals to the brain specifically the medulla oblongata which regulates many homeostatic functions such as respiration and heart function. It sends an impulse into the sinoatrial node through the sympathetic nervous system to increase the heart rate therefore increasing cardiac output. This is done to increase the amount of oxygen in the muscles during aerobic respiration, Baroreceptors in the blood that detect the change in heart rate increase the blood pressure via vasodilation (widening of the blood vessels) to allow more blood to be carried.

Doing any repetitive exercise, the muscles being used will experience muscle fatigue which is reduction in their capacity to do work. This may be due to the production of lactic acid when anaerobic respiration takes place and there is significant ATP depletion with little ATP production.

The aims of this experiment are as follows: Aim 1-Examine the feasibility of using a large cohort of investigators to collect data for a force fatigue curve in grip strength protocol, Aim 2- Establish the effect of this grip strength protocol on the blood pressure response, Aim 3- Examine the association between maximal grip strength and fat free mass.

Moreover, the hypotheses of this experiment were: Hypothesis 1- Using large cohorts of investigators to collect data is feasible, Hypothesis 2- Repeated Grip strength will cause an increase in blood pressure, Hypothesis 3- A higher maximum grip strength will be achieved by those that have higher fat free mass.

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Equipment: sphygmomanometer (used to measure blood pressure), scale (used to measure weight), stadiometer (used to measure height), omron handheld body fat analyser (used to measure body fat percentage), dynamometer (used to measure grip strength), stopwatch (to measure time).

Procedure: Initially volunteer’s blood pressure is taken at rest while seated, from their dominant arm that was later used for the grip strength segment. The blood pressure cuff was placed on the participants upper arm (just above the elbow) ensuring that it is not covered by any thick clothing/material and as close to the skin as possible. The cuff was secured on to arm by tightening it and wrapping it around the arm, whilst ensuring that the lead was positioned facing toward the inner elbow in order to be closest to the brachial artery (for accurate data), while the participants arm rested on a table so that it was parallel to their heart. Blood pressure (systolic and diastolic) as well as heart rate was recorded. Participants’ shoes were removed and their weight (in kg) was recorded using a scale and their height taken (in cm) using a stadiometer. The shoes were removed to ensure that there was no extra height added by them. In addition, any extra heavy clothing such as jackets or anything that may add extra weight to the volunteer was also removed before their weight was taken from the scale. Finally, the participants age, height and weight were input into the handheld body fat analyser before being held up horizontally in front of the participant (by the participant) while seated, their body fat was measured by the machine, and the data was recorded. A Par-Q form with 7 questions was filled out by the volunteers to ensure that anyone with a relevant health condition did not take place in the experiment if it would be a risk to their health, and prevent the data being collected from being skewed.

The experiment began while the volunteer was seated in an upright position holding the dynamometer in their dominant hand while their arms were positioned straight down (vertically). The participant then squeezed the dynamometer at maximum strength and the measurement recorded into a table. This was repeated every 30 seconds using a stopwatch and recording the data for 10 minutes. 21 measurements of maximal isometric grip strength were recorded in total (participant was instructed to use maximum strength when gripping the dynamometer).

Lastly immediately post the experiment the volunteer’s blood pressure was taken again using the same dominant arm used to grip the dynamometer and the results were recorded.

The results below (figure 1) show that grip strength for most of the participants remained mainly linear, as the time increased there wasn’t much change in the mean hand grip strength.

The results in Figure 1 are mainly linear showing that there wasn’t much change in the mean grip strength over time. This may be due to a variety of reasons, for example this specific protocol did not account for the difference in data due to gender (male/female grip strength) which could have shown different results. In addition, factors such as age were not accounted for in this protocol which can affect the data as seen in (Charlton et al., 2015) which showed that both right- and left-hand overall grip strength decreases with age. It also didn’t account for the variation in hand sizes and how much the fingers were spread out in order to achieve maximum control of dynamometer. As a result of having many uncontrolled variables in this protocol the results in Figure 1 were unable to be matched with any other published work. Consequently Hypothesis 1 could only be achieved if the protocol was adjusted and accounted for the many dependant variables.