Biomechanics Lab Report example PDF

Preview

Summary

Laboratory Report
The effect of arm swing on countermovement jump
...

Description

Department of Exercise and Sport Science Biomechanics 2

Laboratory Report The effect of arm swing on countermovement jump

1. Introduction Vertical countermovement jumping to attain maximal height is an important action for enhanced performance in sport such as basketball and volleyball (Umberger, 1998). According to Cheng et al. (2008), people are accustomed to jumping with an arm swing which suggests jumps without an arm swing may not be optimal in attaining maximum height. Moreover, previous findings have shown that arm swing facilitated an increase of above 10% in jump height (Shetty and Etnyre, 1989; Harman et al., 1990; Feltner et al., 1999). Cheng et al. (2008) found that increased take-off (TO) velocity of the centre of mass (CoM) contributed nearly two thirds to increased jump height which also reflected Lees et al.’s findings of 72% contribution to increased jump height (2004). Further research has been conducted as to what exactly causes the effect of arm swing to increase jump height through increased TO velocity. Hara et al. (2006) suggested that increased jump height was due to increased activity of the lower extremity muscles from the additional load on the lower extremity from an arm swing. It was noted that increased work by the hip suggested an increased activation of the biceps femoris, which acts as a hip extensor (Umberger, 1998). However, this was not validated as this study did not directly examine electromyography (EMG) which would have been beneficial in determining individual muscle activity in different types of jump (Rota et al., 2013). Although Hara et al.’s study did examine the effect of arm swing during maximal jumping, squat jumps were performed thus not making this study a direct representation of countermovement jumps which would have provided more concrete research for this specific topic. Although the direct study of EMG in countermovement jumping with an arm swing is limited, Lees et al. (2004) found some interaction between muscle activity and arm swing, especially for muscles acting at the hip which would support Hara et al.’s assumption.

However, Lees et al. found a significant decrease in biceps femoris activity. Furthermore, Lees et al. concluded that increased height and TO velocity from arm swing was not exclusively due to the different levels of activity in the lower extremity muscles but rather to a complex series of mechanisms acting collectively. Nonetheless, this study could have provided a more in depth EMG analysis. Payne et al. (1968, cited in Lees et al. 2004) proposed the ‘transmission of force’ theory as the explanation for the increased TO velocity due to arm swing. This theory suggests a greater impulse is produced as vertical ground reaction force (GRF) is increased due to a downward force acting on the body as the arms are propelled upwards. However, Dapena (1999, cited in Cheng et al., 2008) viewed this theory as too simplistic in a simulation investigation. Additionally, Feltner et al. (2004) reported that greater impulse was not due to increased vertical GRF but rather a complex series of mechanisms which supported Lees et al.’s conclusion (2004). However, according to more recent findings, Akl (2013) suggested the use of arm swing contributed to augmented jump height through the acquisition of additional impulse. This was due to increased maximal vertical GRF, which was also found to have a strong correlation with arm swing during countermovement jumping. This study reflected the previous research of Harman et al. (1990) who reported greater vertical GRF, resulting in an increased net impulse, being the direct cause for increased jump height. The purpose of this report is to support the findings that arm swing does enhance performance during a countermovement jump and to investigate and examine further the mechanisms behind this, based on previous published research.

2. Method 2.1. Participants Thirteen injury-free undergraduate students (mean ± S.D.: age = 20.5 ± 2.1 years; stature = 1.77 ± 0.1 m; mass = 74.4 ± 13.2 kg) were required to perform two variations of maximal countermovement vertical jump. There were eleven male participants and two female participants, all wearing shoes. All trials were to follow the same protocol and procedure. The participants were made aware of the purpose and risks of the experiment and gave their written informed consent. 2.2. Apparatus and procedures A Kistler 9281B force plate, recording at 500 Hz, was used to record GRF with Bioware software. An amplifier was used to strengthen the signal and A/D converter to digitise the data to the computer. While on the force plate, the participant’s body mass would be subtracted using the Bioware software so that GRF would be set at a constant zero before each jump. A Delsys Bagnoli 8 channel box, recording at 1000 Hz was used to record raw EMG readings from lower extremity muscles with EMGWorks 4.1 software. An amplifier was used to strengthen the signal and A/D converter to digitise the data to the computer. The weight of the channel box was negligible therefore would not have a significant effect on the mass of the participant. Both the force plate and EMG equipment were synchronised to the computer to record data simultaneously during a window of 5 seconds from the touch of a button (Figure. 1).

Figure 1. Experimental set-up of equipment and procedure. The participants performed a maximal vertical jump on the force plate two different ways (Figure. 2): countermovement jump with arm swing (CMJAS) and countermovement jump without arm swing (CMJ). A countermovement jump is a type of bilateral vertical jump, that incorporates a stretch-shortening cycle (Magee et al., 2007), with preceding flexion of the ankle, knee and hip joints and subsequent extension of these briefly flexed joints (Radcliffe and Farentinos, 1999). CMJ was performed with hands placed on the iliac crest to minimise arm movement.

(Gardner et al., 2012) Figure 2. Positions of the body during CMJAS and CMJ. The rectus femoris (RF) and biceps femoris (BF) were marked because these biarticular muscles act to flex and extend both the hip and knee which are essential movements for jumping (Umberger, 1998).

To reduce the effect of cross-talk, these muscles were identified through performing a seated isometric knee extension and lying hip extension respectively against manual resistance and then palpating the belly of the muscle. The surface of the skin was shaved and cleansed with ethanol wipes before placing the mono-polar electrodes over it with the wires facing upwards. A reference electrode was placed over the bony prominence of the patella. These were connected to the Delsys Bagnoli 8 channel box, tucked in the participant’s shorts. Following appropriate warm-up and familiarity with the movement, three successful trials for CMJAS were first completed followed by three successful trials for CMJ. There was a rest period of approximately two minutes between trials to maximise jump performance. The data from each participant’s final trial of each jump condition was to be analysed. Finally, an isometric maximal voluntary contraction (MVC) was recorded for the RF and BF from performing a seated knee extension and lying hip extension respectively against manual resistance. 2.3. Analysis The dependent variables to be analysed were duration of TO phase, duration of flight phase, minimal vertical GRF, maximal vertical GRF, net impulse, TO velocity of CoM, jump height, peak average rectified EMG (PAVEMG) and normalised EMG for each muscle and total PAVEMG. In order to calculate temporal variables, vertical GRF was processed in a spreadsheet. The start and end points of both TO and flight phase were noted by visually identifying significant changes in vertical GRF patterns. Thus, the difference between the start and end points of each phase represented the duration of each phase. For vertical GRF data, the minimum and maximum values were identified using a spreadsheet. Net impulse was calculated through the following equation: impulse (N∙s) = F∙∆t. Thereafter, take-off velocity was subsequently calculated through the impulse-

momentum relationship (Hamill and Knutzen, 2008), also known as Newton’s Second Law of Motion: F∙∆t = m∙∆v ∴ ∆v =

.

Finally, jump height was calculated through an equation of Uniformly Accelerated Motion (Linthorne, 2001), procured by Galileo: where g = -9.81 m s-2. Raw EMG and MVC data was processed into AVEMG using a spreadsheet by converting all of the data into absolute values and calculating the mean. In order to compare the level of muscle activity from the jumps as a percentage of muscle activity from the MVCs, EMG data was normalised through the following equation: Normalised EMG (%MVC) = ∙100 Normalised EMG would also verify the accuracy of the raw EMG recordings by assuming the MVCs would be greater than the PAVEMG recorded from the jumps. Descriptive statistics were implemented on IBM SPSS to calculate the mean and standard deviation of each variable and to determine the normality of the data through Skewness, Kurtosis and Shapiro-Wilk. The difference of the variables between the two jump conditions was also determined through paired samples T-tests since the same group of people performed both conditions. If parametric assumptions were broken due to nonnormally distributed data, a Wilcoxon-Signed Ranks test (statistic Z) was used. A value of p ≤ 0.05 was used to represent statistical difference.

3. Results

Table 1 displays the points in time and duration of the TO and flight phases in both jump conditions. TO duration was greater in CMJ than CMJAS by 0.02 s, but with nonsignificant difference (p > 0.05). This indicates there was greater duration spent performing countermovement and TO during CMJ. However, flight duration was significantly greater in CMJAS than CMJ by 0.04 s (Z = 2.981, p < 0.05). This indicates that there was greater duration spent airborne during CMJAS. Table 1. Mean (±S.D.) temporal data associated with two different jump conditions (N=13). CMJ CMJ AS Mean SD Mean SD TO phase Start (s) 0.84 0.34 0.82 0.22 End (s) 1.72 0.36 1.72 0.25 Duration (s) 0.88 0.20 0.90 0.14** Flight phase End (s) 2.30 0.39 2.24 0.27 Duration (s) 0.58 0.11 0.52 0.06 * * indicates a significant difference between the CMJAS and CMJ condition (p < 0.005). **indicates a non-significant difference between the CMJAS and CMJ condition (p > 0.005).

Table 2 displays the kinetic variables and figure 3 displays the net impulse in both jump conditions. CMJAS produced significantly greater jump height by the CoM than CMJ by 0.07 m (Z = 3.19, p ≤ 0.001). CMJAS also produced significantly greater TO velocity than CMJ by 0.25 m·s-1 (p < 0.001). The maximal vertical GRF value was significantly greater (p ≤ 0.05) in CMJAS than CMJ by 87 N (0.12 BW) and the minimal value was lower in CMJ than CMJAS by 21 N (0.04 BW), but with non-significant difference (p > 0.05). Furthermore, net impulse was significantly greater in CMJAS than CMJ by 18.9 N·s (p ≤ 0.001). Figure 4 depicts one participant’s vertical GRF pattern (Fz in Figure 4) application over time, which displays greater maximal vertical GRF of 1099 N for CMJAS compared to that of 917 N for CMJ and lower minimal vertical GRF of -589 N for CMJ compared to that of -412 N for CMJAS. This was a true reflection of the greater mean maximal vertical GRF in CMJAS and lower mean minimal vertical GRF in CMJ. Table 2. Mean (±S.D.) kinetic data associated with two different jump conditions (N=13).

CMJAS CMJ Mean SD Mean SD Minimum (N) -442 202.4 -463 192.9 ** (BW) -0.39 0.53 -0.35 0.58 Maximum (N) 1021 193.8 934 182.5 * (BW) 1.42 0.26 1.30 0.24 Net impulse (N∙s) 201.8 46.3 182.9 42.0 * T/O velocity (m∙s-1) 2.70 0.3 2.45 0.3 * Jump height (m) 0.38 0.1 0.31 0.1 * * indicates a significant difference between the CMJAS and CMJ condition (p ≤ 0.005). **indicates a non-significant difference between the CMJAS and CMJ condition (p > 0.005).

210

* 200

Impulse (N∙s)

190

180

170

160

150

CMJAS

CMJ

Figure 3. Mean (±S.D.) net impulse associated with two different jump conditions (N=13). * indicates a significant difference between the CMJAS and CMJ condition (p < 0.001).

1500 CMJ

CMJAS

1000

Fz (N)

500

0. 50 0. 2 55 0. 0 59 0. 8 6 0. 46 69 0. 4 74 0. 2 7 0. 90 83 0. 8 88 0. 6 93 0. 4 9 1. 82 03 1. 0 0 1. 78 12 1. 6 17 1. 4 22 1. 2 27 1. 0 3 1. 18 36 1. 6 41 1. 4 46 1. 2 51 1. 0 5 1. 58 60 1. 6 65 1. 4 70 1. 2 7 1. 50 79 1. 8 84 1. 6 89 1. 4 94 2

0

-500

-1000

Time (s)

Figure 4. Vertical GRF plotted against time at TO during two different jump conditions.

PAVEMG for RF was greater for CMJ than CMJAS by 0.0348 mV (Table. 3) but with non-significant difference (Z = -0.384, p > 0.05). Therefore, the normalised EMG for RF was greater by 5% for CMJ, which was 112%, than CMJAS, which was 107%, with nonsignificant difference (Z = 0.944, p > 0.05). This suggests RF muscle activity was greater during both jump conditions than during MVC. PAVEMG for BF was greater for CMJAS than CMJ by 0.1368 mV but with nonsignificant difference (Z = 1.503, p > 0.05). Therefore, the normalised EMG for BF was greater by 10% for CMJAS, which was 49%, than CMJ, which was 39%, but with significant difference (p ≤ 0.05). This suggests BF muscle activity was lower during both jump conditions than during MVC. Total PAVEMG for both muscles was greater for CMJAS than CMJ by 0.1019 mV with non-significant difference (Z = -0.384, p > 0.05). This suggests greater muscle activity occurred in the lower extremity during CMJAS.

Table 3. Mean (±S.D.) EMG data associated with two different jump conditions (N=13). CMJAS CMJ Mean SD Mean SD PAVEMG RF (mV) 0.3356 0.3 0.3704 0.3 ** Normalised RF (%) 107 30.3 112 37.6 ** PAVEMG BF (mV) 0.3118 0.4 0.1750 0.2 ** Normalised BF % 49 13.7 39 12.4 * Total PAVEMG (mV) 0.6474 0.6 0.5455 0.5 ** * indicates a significant difference between the CMJAS and CMJ condition (p ≤ 0.05). **indicates a non-significant difference between the CMJAS and CMJ condition (p > 0.05).

Discussion Results confirmed that CMJAS produced a greater enhancement in performance than CMJ and provided further insight and points for discussion on the mechanisms behind this effect. Current values for temporal and kinetic variables displaying significant difference were directly compared with values of previous related investigations in order to compare outcome and similarity of results. CMJAS produced significant increase in flight phase duration with 0.58 s compared to CMJ with 0.52 s. Harrison and Moroney (2007) displayed results also between 0.50 s and 0.60 s for both conditions with the same outcome, stating jump performance was determined by flight time. CMJAS produced significant increase in jump height with 0.38 m compared to CMJ with 0.31 m while Lees et al. (2004) procured similar results of 0.39 m and 0.33 m for CMJAS and CMJ respectively. This increase of approximately 23% relates to previous findings which have shown that arm swing facilitated an increase above 10% (Shetty and Etnyre, 1989; Harman et al., 1990; Feltner et al., 1999). According to Cheng et al. (2008), increased TO velocity of the CoM contributed nearly two thirds to increased jump height which also reflected 72% contribution in Lees et al (2004). CMJAS produced significant increase in TO velocity with 2.70 m·s-1 compared to CMJ with 2.45 m·s-1 while Hara et al. (2006) procured similar results of 2.73 m·s-1 and 2.46 m·s-1 for CMJAS and CMJ respectively.

To investigate the explanation for increased TO velocity due to arm swing, net impulse was analysed. CMJAS produced significant increase in net impulse with 201.8 N·s compared to CMJ with 182.9 N·s while Akl (2013) procured related net impulses of 233.6 N·s and 219.0 N·s for CMJAS and CMJ respectively. Impulse is dependent on the quantity of force application as it is the product of force multiplied by change in time (Hamill and Knutzen, 2008). Therefore, since net impulse was greater in CMJAS than CMJ, maximal vertical GRF was also significantly greater with 1021 N for CMJAS compared to 934 N for CMJ. These were similar to those from Akl (2013) with 1236 N and 956 N for CMAS and CMJ respectively and were therefore analysed in the same unit of measurement. These support the assumptions of Payne et al. (1968, cited in Lees et al. 2004) and Harman et al. (1990) which depict the ‘transmission of force’ theory which further suggests greater vertical GRF resulting in increased net impulse as being the direct cause for increased jump height. Additionally, this is reciprocated by Dowling and Vamos (1993) who reported that a high maximum force was necessary for enhanced performance and that the pattern of force application was the most crucial aspect in vertical jump performance. However, it was also noted that high maximal force was also not sufficient for enhanced performance. This suggests a complex series of mechanisms is responsible for increased TO velocity due to arm swing which meets the assumption of Feltner et al. (2004). Rota et al. (2013) reported that investigating EMG would be beneficial in determining individual muscle activity in different jump conditions. However, normalised EMG appeared inaccurate because mean RF values for both jump conditions were greater than MVC, which may reflect data error. Due limited EMG-related studies on this particular topic, current values could not be directly compared with values from previous studies even in Lees et al. where EMG was only reported in figure format and change of percentage. Therefore,

outcome of results was compared for variables displaying both significant and non-significant difference. PAVEMG and normalised EMG for RF were greater for CMJ than CMJAS, but with non-significant difference to further emphasise this statement while Lees et al. also reported a slight increase with non-significant difference. PAVEMG and normalised EMG for BF were greater for CMJAS than CMJ while Lees et al. reported significant decrease in BF activity. It was noted that PAVEMG produced non-significant difference while normalised EMG produced significant difference, which might reflect data error. However, Hara et al.’s investigation (2006) contradicts Lees et al.’s findings but matches this study in terms of increased BF activation as it was suggested that increased work by the hip increased involvement of this hip extensor due to increased activity of lower extremity muscles from the additional load on the lower extremity due to arm swing. This was also supported by the findings of Blache and Monteil (2012) who concluded that greater muscle work was due to increased activity for the BF. It was noted for this assumption that Hara et al. (2006) did not directly examine EMG and squat jumps were performed thus not making this study a direct representation of countermovement jumps. Nonetheless, it supports the ‘joint work augmentation’ theory where greater muscle force is produced due to the force-velocity relationship in which upward acceleration of the arms can trigger a downward reaction force to act on the rest of the body. Lees et al.’s investigation (2004) further contradicts this theory because lower joint power was produced during jumps with arm swing. However, increased total PAVEMG in this study suggests greater muscle activity produced from the lower extremity as reported as corresponding to joint activation in Bobbert and Cassius (2005, cited in Cheng et al. 2008).

Hara et al. (2006) also stated arm swing to act as an additional load due partly to increased shoulder joint torque applied to the trunk. However, Cheng et al. (2008) later argued that this force on the shoulders is not closely related to changes in vertical GRF, thus supporting Lees et al. (2004) in questioning the ‘transmission of force’ theory. Cheng et al. also questioned the ‘joint work augmentation’ theory as this o...