Power, Strength, and Performance
Harnessing the Musculoskeletal System

Lab II – Power, Strength, and Performance:
Harnessing the Musculoskeletal System

Introduction:

The musculoskeletal system is comprised of muscles and bones and serves the following purposes—support, protection, and ambulation. Even though the various movements performed in this lab require bone function (as do all movements), the focus of this lab will be the role of muscles. Muscles do work and induce movement through contractions (shortening and lengthening of muscle fibers). This is caused in the cellular level by the interactions between myosin fibers with thinner action fibers. The formation of cross bridges and the pulling action by the myosin “arms” create the force that is seen as a muscle contraction. Contractions can be placed in two broad groups—static or isometric and dynamic. Static contractions are not accompanied with movement around the joint. On the other hand, dynamic contractions involve movement around one or more joints. More specific groups of contractions include isotonic contractions and isokinetic contractions. Isotonic contractionsinvolve the use of a constant load (as in free weight exercises), while isokinetic contractions involve constant angular rotation around a joint, meaning that the load moves at a constant speed. Apart from the various classifications described above, contractions can either be concentric or eccentric. This further specifies the contraction as either producing a force while shortening (concentric) or producing a force while lengthening (eccentric).

This experiment will involve the measuring of muscle strength through the use of a few techniques. Strength in this case is defined as the maximal force that can be produced by a muscle or muscle group. The most direct of measuring this strength is through the direct 1-RM test, or the one repetition maximum 1-RM test. In this test, progressively heavier weights are lifted, one at a time with rests in between, until a full repetition can no longer be done. This can be very time-consuming and inefficient in which case the indirect 1-RM test can be performed. The indirect version of the 1-RM makes use of equations that describe the relationship between the percent of 1-RM performed and the number of repetitions. The handgrip test will also be used to give another measure of estimated overall strength. This test measures isometric strength of the forearm flexors.
It is important tonote that muscle strength is not directly correlated to muscle power and endurance. Power is known to be more closely related to the functional activity being performed as well as muscle fiber type being used. The Wingate anaerobic power test will be used to estimate the muscle power of the subject. Muscle fibers are separated into two main groups, slow twitch and fast twitch. Slow twitch fibers contain a higher percentage of mitochondria as well as an increased level of myoglobin and blood capillaries. This allows for high oxidative capacity (aerobic) and a resistance to fatigue. Because of this, these fibers are used during long-term endurance activities. Fast twitch fibers on the other hand contract rapidly and come in two forms, type IIa and type IIb. Type IIa fibers contain a good amount of mitochondria and myoglobin leading to a medium oxidative capacity and a medium resistance to fatigue. Conversely, type IIb fibers have a low mitochondria and myoglobin composition leading to a low oxidative capacity. These are mostly used for very short-term, very high power activities relying on anaerobic energy pathways.
The purpose of this lab is to measure and analyze the muscle strength and power of an individual through the use 3 techniques: the handgrip test, the indirect 1-RM test, and the Wingate anaerobic power test. Ibelieve that the two strength tests do provide a valid estimation of the subject’s strength, with the indirect 1-RM test being more accurate as it is based on the direct 1-RM. I hypothesize that muscular strength is lower in females than in males due to increased muscle mass in males. I also hypothesize that even though males might have a greater start power, females will have a higher endurance. Furthermore, I hypothesize that an increased body mass (constant height) leads to a decrease in muscular strength and power. I also believe that the Wingate test will not give be a completely proper way to measure anaerobic power since the only muscles involved are the legs—the anaerobic power stored in the upper extremities is not harnessed.

Methods
Hand grip dynamometry procedure:
First, the dynamometer will be adjusted into a proper and comfortable position for the subject. This will include a quick calibration to make sure the needle counter is set to 0. In preparation for the test, the subject will stand erect and then squeeze the dynamometer as hard as possible without any body movement. The process will be run 3 times on each hand (with 30 second rest between each run) and each measurement will be recorded. After 3 trials, each value in kg will be converted into N. The highest score will be used to classify fitnesslevel. The relative force is then calculated by dividing the force (kg) over the body weight (kg). Finally, the % difference between the dominant and non-dominant hands will be calculated.

Indirect 1-RM procedure
First, the dumbbell weight must be calculated by multiplying the body weight by 0.125 (this dumbbell weight is about 1/8 of the body weight). The subject should do as many repetitions are possible from a position starting at 180° and ending in a complete motion (around 20°). Repetitions should be smooth without any generation of momentum. If the subject is about to finish the 20 maximum reps, he/she should stop, rest, and start again with a higher weight. After this, the same test should be run starting again from 180° to only 90°. Finally the 1-RM will be calculated with the achieved repetitions and the known body weight with the following equation
1RM=rep30+1×weight in kg of dumbell
Wingate Anaerobic Power Test procedure:
First, the subject’s body weight must be measured. The cycle ergometer must be adjusted comfortably for the subject performing the test. The resistance applied needs to be calculated by multiplying the subject’s body weight by 0.075. Once the subject is seated on the bike, he/she will start pedaling as fast as possible. As soon as pedaling starts, the resistance should be applied.Simultaneously, the number of revolution made every 5 seconds should be recorded. These observations should be done until the subject can no longer pedal. After the test, the anaerobic power will be calculated for each 5 second interval using the following equation
resistance×6m×revs0.083 min=anaerobic power

Results:
Hand grip dynamometry:
Subject was a 21 year old male, weighing 77 (kg) with a height of 168 (cm).

Table 1: Strength Tests (absolute force)
| Trial 1 (kg) | Trial 2 (kg) | Trial 3(kg) | Best (kg) | Best (N) |
Dominant Hand | 46 | 45 | 48 | 48 | 480 |
Non-Dominant Hand | 37 | 35 | 38 | 38 | 380 |

Table 2: Relative force and absolute ratings
Relative force, dominant hand | .623 (kg) | 6.23 (N) |
Relative force, non-dominant hand | .494 (kg) | 4.94 (N) |
% difference between dominant and non-dominant hands | 23.26% |
Rating for dominant hand | Average |
Rating for non-dominant hand | Very poor |
% of normal value | 83.5% of normal value |

Calculations:
Kilogram conversion to N:

48 kg×10ms2=480 N
38 kg×10ms2=380 N
Relative force:

48 kg77 bw in kg=0.623 kg×10(ms2=6.23 N (dominant hand)
38 kg77 bw in kg=0.494 kg×10(ms2=4.94 N (non-dominant hand)

% difference between dominant and non-dominant hands:

48-3848+382×100=23.26%

% of normal value:

86103×100=83.5%

Indirect1-RM:

This test was performed on one male and one female—results for both will be presented.

Male weighed 80 kg and had a height of 168 cm.

Table 3: 1-RM measurements for male subject
(180 degrees – 20 degrees) | 12 reps at 30 lbs. (13.6 kg) |
(90 degrees – 20 degrees) | 19 reps at 30 lbs. (13.6 kg) |
1-RM (180 – 20) | 19.04 (kg) | Relative force=0.238 (kg) | 190.4 (N) |
1-RM (90 – 20) | 22.21 (kg) | Relative force=0.278 (kg) | 222.1 (N) |
Calculations:

Dumbbell lift:
175 body weight in lbs.×0.125=~20 lbs

1-RM calculation (180-20):

12 reps30+1×13.6weight of dumbbell in kg=19.04kg
1-RM calculation (90-20)
19 reps30+1×13.6weight of dumbbell in kg=22.21kg

Female weighed 75 kg and had a height of 168 cm.

Table 4: 1-RM measurements for female subject
(180 degrees – 2 degrees) | 7 reps at 20 lbs. (9.1 kg) |
(90 degrees – 20 degrees) | 20 reps at 20 lbs. (9.1 kg) |
1-RM (180-20) | 11.2 (kg) | Relative force=0.149 (kg) | 112.2 (N) |
1-RM (90-20) | 15.2 (kg) | Relative force=0.202 (kg) | 151.6 (N) |

Calculations:

Dumbbell to lift:

165 body weight in lbs.×0.125=~20 lbs.

1-RM calculation (180-20):
7 reps30+1×9.1weight of dumbbell in kg=11.2kg
1-RM calculation (90-20):
20 reps30+1×9.1weight of dumbbell in kg=15.2kg
Wingate Anaerobic Power

The test was performed by both amale and a female—both results will be presented.

Male subject weighed 79.5 kg.

Body weight times 0.075 = 6 kg of resistance

Table 5: Male Wingate Data
Time | 1-5 sec | 6-10 sec | 11-15 sec | 16-20 sec | 21-25 sec | 25-30 sec |
Number of revs | 16 | 12 | 11 | 11 | 6 | 11 |
Anaerobic power (kgm/min) | 6939 | 5204 | 4771 | 4771 | 2602 | 4771 |
Anaerobic power (W) | 1134 | 850 | 780 | 780 | 425 | 780 |
Anaerobic power (W/kg) | 14.3 | 10.7 | 9.8 | 9.8 | 5.35 | 9.8 |

Calculations:

Determining resistance:
79.5 kg×0.075=6kg of resistance

Anaerobic power (kgm/min):
(5kg×6m×16)0.083=6939 kgaˆ™mmin
(5kg×6m×12)0.083=5204 kgaˆ™mmin
(5kg×6m×11)0.083=4771 kgaˆ™mmin
(5kg×6m×11)0.083=4771 kgaˆ™mmin
(5kg×6m×6)0.083=2602 kgaˆ™mmin
(5kg×6m×11)0.083=4771 kgaˆ™mmin

Graph 1: Power (Watt) vs. Time for Male Graph 2: Power (Watts/kg) vs. Time for Male

Female subject weighed 63.18 kg.

Body weight times 0.075 = 4.7 (~5 kg of resistance)

Table 6: Female Wingate Data
Time | 1-5 sec | 6-10 sec | 11-15 sec | 16-20 sec | 21-25 sec | 25-30 sec |
Number of revs | 10 | 11 | 8 | 7 | 6 | 7 |
Anaerobic power (kgm/min) | 3614 | 3975 | 2891 | 2530 | 2168 | 2530 |
Anaerobic power (W) | 590 | 649 | 472 | 413 | 354 | 413 |
Anaerobic power (W/kg) | 9.34 | 10.3 | 7.5 | 6.5 | 5.6 | 6.5 |

Graph 3: Power (Watts)vs. Time for Female Graph 4: Power (Watts/kg) vs. Time for Female

Calculations: one sample will be done

Determining resistance:

63.18 kg×0.075=4.7 kg (~5 kg of resistance)

Anaerobic Power calculation:

(5kg×6m×10)0.083=3614 kgaˆ™mmin
(5kg×6m×11)0.083=3975 kgaˆ™mmin
(5kg×6m×8)0.083=2891 kgaˆ™mmin
(5kg×6m×7)0.083=2530 kgaˆ™mmin
(5kg×6m×6)0.083=2168 kgaˆ™mmin
(5kg×6m×7)0.083=2530 kgaˆ™mmin

Discussion:

The presented data shows the measures of strength and power in both males and females. The date supports my hypothesis—males tend to show more muscular strength and power than women. This is demonstrated in the indirect 1-RM test. The male subject was able to lift more weight, more times. Furthermore, data supports my hypothesis that men have greater initial power while women have greater endurance. This was shown in the Wingate anaerobic power test. The male participant started off with greater pedaling force due to larger muscles and larger glycogen reserves, however, the revolution pedaled after each 5 second interval decreased sharply as seen in Graphs 1 and 2. Even though the female counterpart started off with a lesser pedaling power, she was able to maintain the power for longer. This visualized in the shallower slope presented in Graphs 3 and 4.
The first two techniques, tests to measure muscularstrength, cannot be compared to one another in this case because the subjects for each were different. For this reason, the results from each cannot be compared for accuracy. The hand grip test showed that the dominant hand of the subject had a 23.26% greater strength than the non-dominant hand (Table 1). This is usually seen as the dominant hand is the most used—greater fiber density—while the non-dominant hand shows weakness. According to established ratings based on the force produced by the hand squeeze, the subject’s dominant hand rated average while the non-dominant hand rated very poor. The total combined “squeeze force” was 83.5% of the normal general value. The mean for the combined hands is 103kg while the subject’s combined force was 86kg. The subject, according to the data collected, was place in the 20th percentile range. The table of percentiles is dated 1977—this data might not be current with modern procedures leading to inaccurate data. There might have been some error in the data since the recommended break of 1 minute was shortened to 30 seconds. This might have caused a negative correlation with the data gathered.
The indirect 1-RM test supported my hypothesis stating that males have greater muscular strength than females. This was shown by the increased weight carried by the male participant and theincreased number of repetitions performed. Furthermore, in both cases, male and female, it can be seen in Tables 3 4,5,and 6 that more repetitions were done in the 90-20 degrees test. This has a physiological reasoning behind it. In the 180-20 degrees test, the participant had to start raising the dumbbell from a 180 degree position. Muscles do the most efficient work and produce the greatest force at an intermediate length. When the arm is in the 180° position, it must call on the myosin and actin bridges to form. However, the different fibers are too far apart to create and efficient number of cross bridges. For this reason, the force produced is inefficient and weak. AS the arm moves up, the distance between the fibers is shortened and more cross bridges can form, leading to a greater force produced. For this reason, as seen in Table 3, the male subject was able to do 12 reps with a 30 lbs. weight during the 180-20 test—in the 90-20 test he was able to do 19 reps with the same weight. Table 4 shows the same results for the women—she was able to lift a 20 lbs. weight 7 times during the 180-20 test, while being able to lift it 20 times during the 90-20 test. This again is a result of the greater muscle mass (more muscle fibers) present in males. The increased amount of muscle allows for stronger contraction leading to agreater outward force. This can also be explained by the force/velocity relationship of muscles. The maximal amount of weight that can be lifted depends on the initial velocity of the contraction. Velocity and force are inversely proportional—as the velocity of the contraction increases, the force produced decreases. At high velocities, the chemical cascade that initiates myosin/actin cross bridges does not propagate efficiently, leading to a diminished amount of cross bridges, leading to a decreased force. However, at lower velocities, the chemical cascade impacts more sites, leading to more cross bridges, leading to an increase in force. The 1-RM data gathered in these tests are not completely accurate to the participant since the exact determined weight was not used during the tests.
The Wingate test was run by one male and one female. Again because of the greater amount of muscle present in the male, the initial pedaling power was greater at the start. This is seen in Table 5 where the male produced a maximum power of 1134 Watts. Table 6 shows the results for the females Wingate test. Her initial (maximum) power was established at the start of the activity, peaking at 590 Watts. The graphs (1-4) show a very critical difference in the way the body of a male responds to such exercise as opposed to a female’s body. The maleparticipant was able to achieve a higher initial power output as well as a higher output in all intervals; however, as graph 2 indicates, there is a steeper decrease than the similar graph (Graph 4) for the female. The female can keep a comparable higher power for longer without tiring as fast. This might be explained by a higher percentage of β-oxidative enzymes present in the skeletal muscles of females. In a recent study, both men and women were tested for specific oxidative enzyme in charge of FFA metabolism. Results showed that women had a significantly lower RER (0.87) than men (0.91). This results in a more efficient use of fatty acids for metabolism. “The study showed that women have a higher protein content of VLCAD, MCAD, and TFPa than men[…]” (Amy C. Maher, 2010). These enzyme are part of the β-oxidative pathway that mobilizes FFAs for metabolism. The end result of this study—and something seen in the laboratory Wingate test—is that women have a greater ability to endure longer lasting exercise than men.

Works Cited
HS 342/542 Lab Manual. (2012). Boston.
Amy C. Maher, M. A. (2010, August 6). Women Have Higher Protein Content of Beta-Oxidation Enzymes in Skeletal Muscle Than Men. Retrieved February 13, 2012, from PLoS ONE: https://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0012025#s1