Effects Of Theeffects Of Testosterone On The Human Body Addition Of Weight On The Force Produced By Muscles Undergoing Isometric And Isotonic ContractionIf you need assistance with writing your essay, our professional essay writing service is here to help!
Testosterone has an effect even from inside the mother’s womb as it develops the sex of a male’s organs at seven weeks old which also influences the brain making the hypothalamus more enlarged in volume. (Vousden et al., 2018).
Testosterone has advantages to a male’s physical state before and after as not only does it form a male’s organs in conception but also increases at puberty in later development. Testosterone allows the testes to produce and grow, producing regular sperm with levels of testosterone increasing right through puberty. This is shown in a male’s voice, by becoming deeper. Also, growth in pubic hair and muscle density to grow strong and form allowing manly features to show and along with this comes an increase in sexual desires and competitiveness.
In male testosterone increases neurotransmitters which help tissue to grow, which in turn testosterone increases levels of hormone growth, making exercise more likely to build muscle. This is known as Gonadal hormones and as it helps males bulk where females do not bulk as easily. The gonadal hormone is what controls the reproductive functions in testosterone and oestrogen and identifies a woman from a man biologically. (Comer, Gould, & Furnham, n.d.).
While testosterone has its advantages, it also has disadvantages as men with low levels of testosterone may experience erectile dysfunction. A person can feel a loss of confidence, with no sex drive and feel low on energy levels which results in weight gain and sweating of the body as the body is unable to regulate its body temperature. (Yassin & Saad, 2008).
The body temperature stays regulated due to the anterior pituitary gland (frontal gland) as this is under the control of hormones secreted by the hypothalamus (brain). Hormones released from the hypothalamus is sent down the axon, which is then connected to the pituitary gland, then carried to the anterior gland which release tropic hormones. These hormones help keep the body in a regular state. (Jannini, Screponi, Pepe, Giudice, & Benvenga, 1999).
In a response to stress, the hypothalamus in the brain gives a signal to the adrenal glands which then secrete glucocorticoids and cortisol. If levels of cortisol in the blood remain high from constant stress, overuse can result in lower ability to regulate cortisol so lower levels are then produced through overuse due to damage to the hippocampus. This can stop our fight or flight mode and immune response or metabolism, causing aggressive behaviour and stress from the breakdown of several areas. (Carré & Archer, 2018).
There are many arguments over the brains lateralization and what functions take over from the effect of testosterone from male behaviours such as aggression and visuospatial. In a man the hypothalamus contains a cluster of large cells which is known as the sexual dimorphic nucleus, when compared in size to a female’s brain, the males appear to be much larger in size.
As research has already shown, the brain has two sides, left and right. The left for language and right for spatial and non-verbal tasks.
Research carried out by young 1996, (Baxter et al., n.d.) using MRI scans to monitor the brain during language tasks was done to see if there is evidence of reasons to why the male has a larger SDN. This showed that woman used both left and right hemispheres, whilst the male used only the left side. Evidence showed that a male’s brain was influenced by testosterone by working more independently on one side compared to the female’s brain of both sides which shows testosterone can influence lateralization of a man’s brain resulting in the size difference on the SND.
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Research was carried out (Henley, Nunez, & Clemens, 2010) with rats to see the effect of testosterone on the SDN showed similar similarities in the size difference in the brain. This was done by injecting female rats during their early stages of development. Not only did they show aggressive and experimental behaviour later in life, but also young found the size in the SND in males to be larger compared to the females SND. This showed a repeated pattern carried out by Baxter in 2003.
As the study was carried out in a lab by injecting the rats with injections the rats received a higher dosage than what a human would compared to what a human who would receive on a daily basis at steady and natural pace when the body needs it so findings of this where not seen as been as generalizable compared to that in a naturalistic environment which Baxter carried out. Also, another main factor is that animals and humans do not have the same brain structure to start with making the research and validity uncertain and the main factor raised was if it was it right to use animals in such a cruel way.
In the evolutionary approach to gender, it believes that gender role came from our ancestors through needs of survival to reproduce from the environment. So, men hunt, and woman stay at home to nurture the children, meaning genes are coded. The biological approach to gender argues that nature and nurture both play roles in development. The suggest that gender is determined by certain events from exposure to prenatal hormones and postnatal labelling from what gender they are. (Miller, 2016).
Regardless of nature or nurture or testosterone in pre-stages, are we as a modern society doomed to fail as woman, men been more competitive, whether it is an evolutionary one, leaving our genes to play fate subject to a hormone or a biological one coming from social labelling after genitals, regardless both gender play crucial roles in future development of a child as we have seen proof of this through evolving in numbers.
References
- Baxter, L. C., Saykin, A. J., Flashman, L. A., Johnson, S. C., Guerin, S. J., Babcock, D. R., & Wishart, H. A. (n.d.). Sex differences in semantic language processing: A functional MRI study. Retrieved from www.elsevier.com/locate/b&l
- Carré, J. M., & Archer, J. (2018). Testosterone and human behavior: the role of individual and contextual variables. Current Opinion in Psychology, 19, 149–153. https://doi.org/10.1016/j.copsyc.2017.03.021
- Comer, R. J., Gould, E., & Furnham, A. (n.d.). Psychology. Retrieved from https://catalogue.sunderland.ac.uk/items/385593?query=psychology+ronald+comer&resultsUri=items%3Fquery%3Dpsychology%2Bronald%2Bcomer
- Henley, C. L., Nunez, A. A., & Clemens, L. G. (2010). Exogenous androgen during development alters adult partner preference and mating behavior in gonadally intact male rats. Hormones and Behavior, 57, 488–495. https://doi.org/10.1016/j.yhbeh.2010.02.007
- Jannini, E. A., Screponi, E., Pepe, M., Giudice, F. L. O., & Benvenga, S. (1999). Lack of sexual activity from erectile dysfunction is associated with a reversible reduction in serum testosterone, 392, 385–392.
- Miller, C. F. (2016). Gender Development, Theories of. The Wiley Blackwell Encyclopedia of Gender and Sexuality Studies, (April), 1–6. https://doi.org/10.1002/9781118663219.wbegss590
- Vousden, D. A., Corre, C., Spring, S., Qiu, L. R., Metcalf, A., Cox, E., … Palmert, M. R. (2018). Impact of X/Y genes and sex hormones on mouse neuroanatomy. NeuroImage, 173, 551–563. https://doi.org/10.1016/j.neuroimage.2018.02.051
- Yassin, A. A., & Saad, F. (2008). Testosterone and Erectile Dysfunction. Journal of Andrology, 29(6), 593–604. https://doi.org/10.2164/jandrol.107.004630
Investigating the Effects of the Addition of Weight on the Force Produced by Muscles Undergoing Isometric and Isotonic Contraction.
Abstract:
The forces produced by isometric contractions within the human biceps and triceps muscles as well as isotonic contractions within the cane toad Sartorius muscle may be altered through the addition of weight. This investigation provides an insight into the production of the force of contraction by differing muscles via the contractile process, influenced by calcium, acetylcholine and ATP in response to the stress of the weight placed upon the muscle. The results demonstrate that force produced by the biceps and triceps through muscle contraction increased as the weight was shifted further from the biceps insertion point. Electrical activity in the biceps increased from 0.15mV when the weight was 54 cm from the insertion point, to 0.81mV when the weight was placed 104 cm away, whereas the triceps increased from 0.07 to 0.24 respectively. The maximum lifting velocity of the cane toad Sartorius muscle drastically decreased as increasing weight was applied to the muscle, beginning at 0.193 mm/ms at 5g, and falling to 0.047 mm/ms when 50g was applied. Therefore, the results gathered indicate that the force generated by muscles may be altered in order to accommodate different stresses, which may further influence such things as its maximum velocity of lift.
Introduction:
Isotonic and Isometric muscle contractions occur due to the interaction of thick myosin and thin actin filaments within myofibrils, known as a cross-bridge interaction (Speranza, 2019). The sliding filament mechanism initiates the cross-bridge interaction between these thick and thin filaments, causing the filaments to overlap, shortening the sarcomeres as the Z lines are drawn towards each other (Speranza, 2019). At the neuromuscular junction, acetylcholine is released, which binds to sarcoplasmic reticulum and thus opens ion channels that allow for calcium ions to flow out (Speranza, 2019) (Johnstone, 2019). Ca2+ works as an initiator for this interaction as it binds to troponin molecules within the thin actin filaments, releasing tropomyosin, and thus allowing for the heads of myosin molecules to attach to the actin binding site. ATP binds to the myosin head during this interaction and as myosin utilises this ATP for energy, it pulls the thin filament towards the M line, allowing the myosin head to detach from the initial actin and onto the next actin, and thus the process repeats. This creates contraction within the muscle (Rice et al., 2008) (Edman and Grieve, 1964) (Speranza, 2019). The contraction of skeletal muscles is dependent on the length-tension relationship and is thus able to be altered through changes in the force produced through contraction as well as the number of motor units recruited (Speranza, 2019).
Figure 1: Overlap of thin actin and thick myosin filaments as a result of the change of length of the sarcomere. Adapted from Reconditi, M., Brunello, E., Fusi, L., Linari, M., Martinez, M., Lombardi, V., Irving, M. and Piazzesi, G. (2014). Sarcomere-length dependence of myosin filament structure in skeletal muscle fibres of the frog. The Journal of Physiology, 592(5), pp.1119-1137.
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Experiment A was conducted in order to determine the effects of the addition of various weights to the force generated by isometric contractions in the human biceps muscle. Additionally, experiment B was done in order to analyse the effects of the addition of weights to the maximum velocity of lift and the force produced by isotonic contractions in cane toad Sartorius muscles. As a result of this, the molecular processes that alter the contraction of the muscle and the force it is able to produce may be analysed. The hypothesis tested stated that as the distance of the weight was increased from the bicep insertion point, the electrical activity of the muscle would increase within the human bicep and triceps muscles as more motor units are recruited (Experiment A). The null hypothesis produced for this experiment stated that there would be no increase in the electrical activity of these two muscles upon increasing the distance of the weight, as no more motor units would be recruited. The other hypothesis that was tested stated that the maximum velocity of lift of the cane toad Sartorius muscle (Experiment B) would decrease upon the addition of weight to the muscle. The null hypothesis formulated for this experiment thus stated that there would be no change in the maximum velocity of lift as weight was added to the muscle.
Methods:
The experimental methods used were gathered from the MEDS2001/PHSI2x07 University of Sydney kuracloud website (syd1.kuracloud.com, 2019)
During experiment A, the subject sat at the table and rested their arm along the edge of the table at a 90-degree angle. The distance of the bicep insertion point to the end of the hand was then recorded. The subject was handed a stick with cable ties placed at 10cm intervals along the stick and was instructed to hold it at the area just before the initial cable tie. A 1kg weight was then moved 10cm along the stick every few seconds whilst the subject attempted to hold the stick stably. The RMS values of the biceps and triceps was then gathered by the EMG and was tabulated.
Experiment B utilised an isolated cane toad Sartorius muscle, whose distal end was connected to a lever so that weights may be applied, and pelvic end connected to a Perspex chamber that was held in place by a palmer stand. The lever was then connected to a fulcrum transducer. 2mm mechanical stops were put in place to avoid overstretching. The weights were then added to the distal end of the muscle in increasing intervals whilst the muscle was stimulated with electrodes. The initial length of the muscle was kept the same for all tests. The fulcrum transducer then measured the lift done by the muscle against the time taken for the lift to occur. The maximum velocity was then calculated and tabulated.
Results:
Analysis of the results gathered from experiments A and B allowed for the investigation of the effects of the addition of weights to the electrical activity, and thus force produced by isometric contraction within the bicep and triceps muscles as well as the maximum velocity of lift produced by the cane toad Sartorius muscle through isometric contraction. As can be viewed in Table 1, both the electrical activity of the bicep and triceps muscles increased as the 1kg weight was moved further from the bicep insertion point. The bicep muscle electrical activity rose drastically more so than that of the triceps muscles, beginning at 0.15mV at 54 cm from the bicep insertion point, and rising to 0.81mV at 124cm from the bicep insertion point, whereas the triceps respectively rose from 0.07mV to 0.24mV. This relationship can be observed through Figure 2. Experiment B however, demonstrated that as the weight placed on the muscle was increased, the maximum velocity of lift produced by the muscle decreased and the muscle was unable to lift the weight as it grew heavier. This can be observed through Table 2, whereby the maximum velocity of lift fell from 0.193 mm/ms at 5 g, to 0.047 mm/ms at 50g.
Table 1: The force generated by the Biceps and Triceps when weight is applied at certain distances from the bicep insertion point.
| Distance of Weight from biceps insertion point (cm) | RMS value for biceps (mV) | RMS value for triceps (mV) |
| 54 | 0.15 | 0.07 |
| 64 | 0.29 | 0.09 |
| 74 | 0.42 | 0.13 |
| 84 | 0.52 | 0.14 |
| 94 | 0.68 | 0.18 |
| 104 | 0.81 | 0.24 |
Figure 2: A comparison of the force generated by the biceps and triceps when weight is applied at increasing length intervals from the elbow joint. A) The electrical activity of the bicep muscle increased dramatically as the weight was moved further from the bicep insertion point. B) The electrical activity of the triceps muscle increased less dramatically than the biceps muscle.
Table 2: The decrease in maximum lift velocity produced by isotonic contraction of cane toad Sartorius muscles when varying levels of weight are applied.
| Weight Applied to the Muscle (g) | Maximum Velocity of Lift Produced Through Isotonic Contraction (mm/ms) |
| 5 | 0.193 |
| 10 | 0.167 |
| 15 | 0.153 |
| 20 | 0.143 |
| 25 | 0.124 |
| 30 | 0.108 |
| 40 | 0.078 |
| 50 | 0.047 |
Figure 3: The maximum velocity of lift produced by the force of the isotonic contraction within the cane toad Sartorius muscle when subjected to various different weights. A) The muscle was provided with an electrical stimulus in order to ensure the contraction of every muscle fibre and thus allowing for cross-bridge cycling to occur. As the weight was increased, the maximum velocity of lift decreased from 0.193mm/ms at 5g of weight to 0.047mm/ms at 50g of weight.
Discussion:
Through analysis of the data gathered from experiments A, it can be observed that the electrical activity of both the biceps and triceps muscles increased as a result of the weight being moved further from the bicep insertion point. This occurred as a result of the need to recruit more motor units to oppose the torque created by the placement of the weight away from the biceps insertion point. The isometric contraction, whereby no muscle lengthening is occurring, that is transpiring within the muscle is caused by the process of excitation-contraction coupling (Speranza, 2019). This process utilises motor neurons to innervate muscle fibres within the body. This causes the release of acetylcholine at the neuromuscular junction, where it binds with the sarcoplasmic reticulum, opening ion channels that allow for the movement of calcium and sodium ions within the muscle. (Speranza, 2019) (Edman and Grieve, 1964). The amount of motor neurons innervating smaller muscle fibres within the body may be increased as a result of the need to increase force produced by the muscle. Sarcomeres within the muscle shorten as a result of this process, whilst the muscle itself doesn’t contract, increasing tension within the muscle and allowing it to produce enough force to counter the load being placed on it (Reconditi et al, 2014) (Speranza, 2019). Thus, electrical activity in the muscle is increased. This result is consistent with the alternative hypothesis that was generated for Experiment A.
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The isotonic contraction that occurs within the cane toad Sartorius muscle however involved the lengthening and shortening of the muscle (eccentric and concentric contractions) to create the force needed to lift the weight that was applied. The maximum velocity of lift of the muscle decreased substantially as the weight applied to the muscle was increased (syd1.kuracloud.com, 2019). The isotonic contraction occurred through electrical signalling, similar to Experiment A. The release of acetylcholine was triggered through constant stimulation to ensure all muscle fibres were producing force. The binding of acetylcholine to the sarcoplasmic reticulum allowed for calcium and sodium to move through the ion channels that were opened (Edman and Grieve, 1964). The calcium allowed for the creation of cross-bridge cycling through its interaction with troponin in the thin actin filaments, removing tropomyosin as a result (Edman and Grieve, 1964). The heads of myosin molecules were thus able to bind to the actin at the actin binding site, utilising ATP hydrolysis as a fuel source at the myosin ATPase site (Reconditi et al, 2011). This creates a power stroke, causing the sarcomeres within the muscle fibres to shorten, thus producing contraction (Speranza, 2019). As the initial length of the muscle was kept the same before each weight was added, the force produced by the muscle through stimulation was the same throughout. However, the increasing weight that was added produced an increase in downward force, up to a point that exceeded the force generated by the muscle (syd1.kuracloud.com, 2019). The release of optimal amounts calcium within the muscle also decreased as the weights were added, increasing the latency period that occurs before contraction, and thus resulting in a decrease in the maximum velocity of lift (Edman and Grieve, 1964). The results gathered from this experiment supported the alternative hypothesis that was generated.
As a result of the experiments being performed one time per individual group, the results gathered may not be valid. This prevented the use of statistical tests to determine the significance of the results that were gathered. In future experiments, larger sample sizes should be used, in conjunction with a minimum of 100 repetitions to provide sufficient data for statistical analysis. This will allow for increased validity and reliability as the significance of the results gathered may be determined and contrasted against the results produced by other studies. As a result of all of this, further research may be undertaken towards this subject to increasing our understanding and to develop new methods and applications of these processes.
The physiological mechanisms involved in the process of muscle contraction may influence the force produced by the muscle as well as the velocity at which the muscle may lift a certain object through the introduction of weights that counteract the force created. The results gathered from this study indicate that as weight is added to a muscle, the force produced by the muscle will increase to counteract the weight, eventually decreasing the velocity of its lift as the weight begins to exceed the force produced by the muscle.
References:
- Dimitriou, M. (2014). Human Muscle Spindle Sensitivity Reflects the Balance of Activity between Antagonistic Muscles. The Journal of Neuroscience, 34(41), pp.13644-13655.
- Edman, K. and Grieve, D. (1964). On the role of calcium in the excitation-contraction process of frog sartorius muscle. The Journal of Physiology, 170(1), pp.138-152.
- Johnstone, D, 2019, Lecture 8: Nerves and Electrical Signalling, Lecture Notes, Key Concepts in Physiology PHSI2007, The University of Sydney, Delivered 13 March 2019.
- Johnstone, D, 2019, Lecture 9: Synaptic Transmission, Lecture Notes, Key Concepts in Physiology PHSI2007, The University of Sydney, Delivered 15 March 2019.
- Linari, M., Brunello, E., Reconditi, M., Fusi, L., Caremani, M., Narayanan, T., Piazzesi, G., Lombardi, V. and Irving, M. (2015). Force generation by skeletal muscle is controlled by mechanosensing in myosin filaments. Nature, 528(7581), pp.276-279.
- Reconditi, M., Brunello, E., Fusi, L., Linari, M., Martinez, M., Lombardi, V., Irving, M. and Piazzesi, G. (2014). Sarcomere-length dependence of myosin filament structure in skeletal muscle fibres of the frog. The Journal of Physiology, 592(5), pp.1119-1137.
- Reconditi, M., Brunello, E., Linari, M., Bianco, P., Narayanan, T., Panine, P., Piazzesi, G., Lombardi, V. and Irving, M. (2011). Motion of myosin head domains during activation and force development in skeletal muscle. Proceedings of the National Academy of Sciences, 108(17), pp.7236-7240.
- Rice, J., Wang, F., Bers, D. and de Tombe, P. (2008). Approximate Model of Cooperative Activation and Crossbridge Cycling in Cardiac Muscle Using Ordinary Differential Equations. Biophysical Journal, 95(5), pp.2368-2390.
- Syd1.kuracloud.com. (2019). Skeletal Muscle: Practical. [online] Available at: https://syd1.kuracloud.com/i/7c51d22c/student/courses/188/runs/103622/preview/page/1 [Accessed 2 May 2019].
- Speranza, T, 2019, Lecture 7: Skeletal Muscle: Mechanisms of Contraction, Lecture Notes, Key Concepts in Physiology PHSI2007, The University of Sydney, Delivered 11 March 2019.
