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Effects of Fatigue in Lower Back Muscles on Basketball Jump Shots and Landings

Authors:

Hui-Ting Lin,

I-Shou University, TW
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Wen-Chieh Kuo,

National Taiwan Normal University, TW
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Yo Chen,

National Pingtung University, TW
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Tang-Yun Lo,

Tamkang University, TW
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Yen-I Li,

I-Shou University, TW
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Jia-Hao Chang

National Taiwan Normal University, TW
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Abstract

Introduction: The aim of this study was to explore effects of fatigue in lower back muscles on the performance of countermovement jumps (CMJ), jump shots (JS) and landing impact.

Methods: Twelve male healthy collegiate basketball players (age: 22.8 ± 2.7 yrs, stature: 178.0 ± 5.1 cm, body mass: 74.5 ± 6.8 kg) volunteered to participate in this study. Data were collected utilizing a 3D motion analysis system, force plate, and surface electromyography. Field-goal percentage, the lowest point of the center of mass (CoM), the angles of joints during taking off phase and landing, and the electromyography parameters of the rectus femoris, erector spinae lumbalis, and of the lower limbs when performing CMJ and JS were recorded. Lower back muscle fatigue intervention was introduced and followed by a post-test to explore the effects of fatigue in the lower back muscles. Statistical analysis was performed using paired-samples t-test.

Results: After lower back muscle fatigue, field-goal percentages dropped, and lowest point of CoM was increased during JS. Ankle plantar flexion of the hopping leg during CMJ and JS increased, and their knee flexion angles of the hopping leg were reduced when landing. CMJ and JS changed the contribution ratio of both legs after low back fatigue.

Conclusions: Temporary low back muscles fatigue decreased the athletes’ performance and causes a change in landing strategy.

How to Cite: Lin, H.-T., Kuo, W.-C., Chen, Y., Lo, T.-Y., Li, Y.-I., & Chang, J.-H. (2022). Effects of Fatigue in Lower Back Muscles on Basketball Jump Shots and Landings. Physical Activity and Health, 6(1), 273–286. DOI: http://doi.org/10.5334/paah.199
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  Published on 05 Dec 2022
 Accepted on 10 Oct 2022            Submitted on 28 Jul 2022

1. Introduction

While playing basketball, a high frequency of jumping and landing is carried out by players. With the increased intensity of competition, the occurrence of lower-extremity injuries increases (Birrer, 1994). Lower extremity training has been considered as a focused item in practice to improve jumping performance and to avoid sport injuries (Chaouachi et al., 2009, Birrer, 1994). Other than increasing lower extremity muscle strength, sufficient core strength can support the body’s stability during physical movements (Stephenson; and Swank, 2004) and also increase postural control (Rosenblum and Josman, 2003), causing more precise and stable performances of movements can be achieved.

Core muscles mainly consist of the abdominal and lower back muscles. The function of the core muscles is to maintain spinal stability so that the body and spine are stable when there are movements in the extremities (Richardson et al., 1999, Akuthota and Nadler, 2004). Core stability refers to the capability of controlling the position and movement of the trunk over the pelvis to allow transfer of forces and the control of limbs during activities (Kibler et al., 2006). Additionally, the efficiency in recruiting other body parts can be increased, which promotes trunk stability, strengthens limb activities, reduces sports injuries, and improves performance (Foran, 2001, Rosenblum and Josman, 2003, Tse et al., 2005, Lehman, 2006, Bouisset, 1991). Previous studies have suggested that core stability was weaker for most athletes with sports injuries; the performance of the athletes could be improved by core strength training (Nadler et al., 1998, Oliver and Adams-Blair, 2010, Granacher et al., 2014, Imai et al., 2014). Moreover, the speed, agility and explosive force can also be increased effectively. (Mendes, 2016, Dinc and Ergin, 2019). Thus, core muscle training not only promote the stability of the body but also improve players’ performance (Gamble, 2007).

A common scoring method in basketball is shoot a successful jump shot (JS). In addition to performing basketball JS, the countermovement jump (CMJ) is frequently used in athlete jumping performance to quantify adaptions to training and to monitor neuromuscular readiness and fatigue (Pinfold et al., 2018, Heishman et al., 2020, Lin et al., 2021). Most injuries in the lower extremities occur at the moment of landing during jumping (Dick et al., 2007). For example, the anterior cruciate ligament (ACL) was often at high risk for injury during jump landing due to limited hip, knee and ankle motion in the sagittal plane and greater stiffness (Leppanen et al., 2017, Hewett et al., 2005, Hron et al., 2020). During ACL injury period, athletes had greater knee abduction and hip flexion, and a flatfooted position at initial contact (Quatman et al., 2010, Krosshaug et al., 2007, Boden et al., 2009). Additionally, control capabilities may decrease when muscle was exhausted during games, which influences the maximum strength, explosiveness, and agility of the athlete (Buttelli et al., 1996).

Muscle fatigue becomes an indispensable part of the game that may deteriorate the performance. Previous study had mentioned small to moderate damage in performance tests after fatigue accumulation (Montgomery et al., 2008). Most studies investigated the effect of upper or lower limbs muscle fatigue on the sport performance or motor skills (eg. Jump shot or vertical jump) (Buttelli et al., 1996, Hautier et al., 2000, Okazaki et al., 2015). However, little evidence demonstrated that the effect of core muscle fatigue on athlete performance or physical variables (Tong et al., 2014, Lin et al., 2021). A study reported when the global core muscle fatigue, the running endurance was reduced (Tong et al., 2014). Another study showed one of the global core muscles, rectus abdominis, fatigue significantly decreased the jump height, increased the lowest center of mass (CoM) and caused a change in the landing strategy for volleyball players (Lin et al., 2021).

One of global core muscles, lower back muscles, is the trunk extensor muscles keeping the trunk in an upright position. Trunk extensors also control stability of the trunk in the process of jumping and transfer strength from lower extremities to upper extremities (Kibler et al., 2006), allowing performance of accurate upper extremity motions. Effect of trunk extensor muscle fatigue on lower limb jumping performances and landing load for basketball players is still unknown. Investigation is needed to determine whether lower back muscle fatigue can influence scoring results when performing a JS and may change landing load of lower extremities when landing during jumping. The activation status of the erector spinae lumbalis (ESL) can be acquired from surface electromyography, which can serve as an indicator for lower back muscle degree of activation (Hermens et al., 2000, Lin et al., 2021). Therefore, the aim of this study was to understand the influence of fatigue in the erector spinae lumbalis on jump shots performance, countermovement jumps patterns, and landing impact. It was hypothesized, firstly, field-goal percentage significantly decreased for JS following ESL fatigue. Second, after ESL fatigue, significantly decreased position of the lowest point of the CoM, angle of hip, knee flexion, and ankle dorsiflexion at JS and CMJ. Third, during JS and CMJ landing, there was a significant difference in the contributions of the two legs after ESL fatigue.

2. Materials and Methods

2.1. Participants

The minimal number of subjects required to achieve effect size of 0.9, a power of 0.8, and an alpha level of 0.05 was calculated using G*power 3.1 to be 12 subjects.

Twelve male collegiate basketball players (age: 22.8 ± 2.7 yrs, stature: 178.0 ± 5.1 cm, body mass: 74.5 ± 6.8 kg) were included to participate in this study. Ten participant’s dominant hands were right and two participant’s dominant hands were left. All subjects were assessed to assure they had no back and lower extremities disorder or surgery, and they had no major injuries within last six months. All subjects were informed of the purpose of the study, procedures, and rights before providing written consent in accordance with the Declaration of Helsinki.

2.2. Equipment

A Vicon 3D motion analysis system (T20S, VICON, UK) equipped with 8 infrared high-speed cameras was utilized. The testing motions of each subject were collected and recorded at a frequency of 300 Hz. The ground reaction force (GRF) was collected with two force plates (9287, Kistler, Switzerland; BP600900, AMTI, USA). Information from force plates was measured at a frequency of 1500 Hz through a data acquisition card using the Vicon computer. A Noraxon wireless electromyography system (2400T-G2, Noraxon, USA) simultaneously collected the muscle activation status at a 1500 Hz sampling rate. A standard basketball hoop was used in the study. The force plates were set up near the free-throw line, with the free-throw line passing through the centres of the plates. The experimental setup was illustrated in Figure 1.

Set up for our basketball study
Figure 1 

The experiment set up for this study.

2.3. Procedures

To track and define the joint positions of the extremities, a total of 51 reflective markers were adhered to the subjects’ anatomical landmarks based on the plug-in-gait marker setting for full-body models (Davis III et al., 1991). Electrodes were placed on the skin surface after shaving and cleaning at the locations of the following 12 muscles: rectus abdominis (RA) on both sides, erector spinae lumbalis (ESL) on both sides, left and right rectus femoris (RF), left and right biceps femoris (BF), left and right tibialis anterior (TA), and left and right gastrocnemius (GN) (Hermens et al., 2000). Each subject performed maximal voluntary isometric contraction (MVIC) once for each muscle for 5 seconds. The instructions that were given to participants and the joint positions that were used for each muscle are based on Hislop et al. (Hislop and Montgomery, 2007). Rest of 1-2 minutes after each MVIC was allowed. The order of MVIC for each muscle was listed as above. The electromyograph signals from MVIC of all muscles were measured after the participants fully warmed up (Hermens et al., 2000, Sun et al., 2016). Then, three sessions of prior-test data (kinematic, kinetic, and EMG data) of successful CMJ and JS were collected. In order to purposely fatigue ESL, subjects received ESL fatigue intervention. First, subjects laid their stomach on a Roman chair with a 30º incline with pelvic iliac aligned with the upper end of the Roman chair, and their trunk held at a horizontal position. Each trial subjects raised up to the trunk extension position at a rate of 25 repetitions per minute until they could not continue or could not maintain the frequency of the trunk extension movement (Figure 2). Electromyographs were collected to assess ESL fatigue. After fatigue in the ESL was observed, the post-test was performed immediately to collect three trials of post-test data of successful CMJ and JS. The requirements for the movements of CMJ and JS were described as follows:

(a) Start position: trunk was at horizontal status; (b) End position: trunk was raised up
Figure 2 

(a) Start position: trunk was at horizontal status; (b) End position: trunk was raised up.

  1. CMJ: The subject stood upright with their hands placed on the hips. At the start of the movement, the subjects first bent their knee joints and then jumped straight up as high as possible. After landing, the subject allowed the body to stabilize and then returned to a natural standing posture. The jump was considered successful when the left foot on the 1st force plate and the right foot on the 2nd force plates simultaneously when take-off and when landing (Figure 1).
  2. JS: Each subject started from the start line and prepared to catch the ball. Once the ball was received, each subject took two steps forward and stepped foot on 1st force plate (the left leg) and on 2nd force plate (the right leg), respectively and then jumped to make a jump shot, finally landing on the force plates respectively. In this study, one leg was an axial leg and the other was a hopping leg as was characteristic of the JS. During the two-step approach, the axial leg makes the first step in the JS, and the hopping leg makes the second step. When the body stabilized after landing, the subject then returned to their natural standing posture (Figure 1).

2.4. Data Processing

Visual 3D (C-motion, Rockville, MD, USA) was employed to analyse kinematic and kinetic data. The tracks of the reflective markers and the GRF data were smoothed using a Butterworth 4 stage zero phase shift filter. Noise was filtered using a 10 Hz low-pass filter. The reflective markers were used to establish the coordinate system of the lower limb segment and to determine the instantaneous joint angles (hip, knee, and ankle) during taking off and landing, respectively. The position of the CoM, CoM =  (RASI+LASI2)+(RPSI+LPSI2)2 and the angles of the lower extremity joints were calculated. The zero of the lower limb joint angle was defined as the position when the subjects were in their neutral standing posture. The presentation of the results obtained mainly focused on the sagittal plane. Positive and negative symbols respectively indicate the direction of motion in the hip, knee, and ankle joints (Table 1). Considering the weight differences between subjects, all kinetics data were normalized to the individual’s body weight. The signals were band-pass filtered at 10–500 Hz and smoothed using Root Mean Square. The changes in median frequency and mean amplitude were calculated to confirm the fatigue status of the muscle (Masuda et al., 1999). The formulae for median frequency and mean amplitude were based on Kamen et al (Kamen and Gabriel, 2010). The contribution ratio of each leg was defined as the ratio of vertical GRF of each leg to the total force when the first peak vertical GRF was reached at landing.

Table 1

Positive and negative symbols respectively indicate the direction of motion in the hip, knee, and ankle joints.


POSITIVE (+) NEGATIVE (–)

Hip angle Flexion Extension

Knee angle Extension Flexion

Ankle angle Dorsal flexion Plantar flexion

2.5. Statistical Analysis

All statistical analyses were performed using the SPSS (20.0) software package. The differences in the median frequency of each muscle at first and last movement in the ESL fatigue intervention were compared using the paired-samples t-test. Paired-sample t-tests were also used to compare differences in parameters during CMJ and JS before and after ESL fatigue. Parameters included field-goal percentage (goals in 10 shots), lowest position of the CoM, angles of the lower extremity joints when the knee joint reached the maximum flexion angle, the angles of each joint during taking off and landing in the sagittal plane, and the contribution ratio of each leg at landing. Effect sizes (ES) were calculated in accordance with Cohen’s d ES principles using Microsoft Excel. A commonly classified effect sizes as small (d = 0.2), medium (d = 0.5), and large (d = 0.8) (Lakens, 2013). The significance level was set at α = 0.05.

3. Results

3.1. Erector Spinae Lumbalis Fatigue

During ESL fatigue intervention, the median frequency of the first and the last movement was calculated as the percentage change between the two values. The changes in the median frequency of each measured muscle after ESL fatigue intervention were listed in Table 2. The results indicated that there were significant decreases in the median frequency after ESL fatigue intervention for bilateral ESL (p < 0.01), bilateral BF (p < 0.01), and bilateral RF (right RF p = 0.01; left RF p = 0.02), whereas there were significant increases in the median frequency for the left GN and left RA (p = 0.02; p = 0.04) (Table 2). However, during the ESL fatigue intervention, the mean EMG amplitude of ESL first increased then decreased but not significantly changed.

Table 2

Changes in Median Frequencies Before and After ESL fatigue.


THE FIRST MOVEMENT (HZ) THE LAST MOVEMENT (HZ) PERCENTAGE CHANGE (%) P VALUE

Erector spinae lumbalis (ESL) Right 72.60 ± 15.36 38.74 ± 5.83 –46.63 <.01*

Left 69.09 ± 11.71 37.73 ± 7.37 –45.39 <.01*

Biceps femoris (BF) Right 70.04 ± 12.51 58.28 ± 10.22 –16.80 <.01*

Left 71.05 ± 7.42 56.52 ± 11.54 –20.44 <.01*

Gastrocnemius (GN) Right 81.01 ± 24.60 81.23 ± 30.57 0.28 .960

Left 79.25 ± 27.47 100.77 ± 16.88 27.16 .02*

Rectus abdominis (RA) Right 15.80 ± 4.64 16.73 ± 4.83 5.89 .290

Left 14.24 ± 2.60 15.99 ± 2.25 12.24 .04*

Rectus femoris (RF) Right 58.07 ± 3.11 39.92 ± 14.36 –31.25 .01*

Left 58.21 ± 14.69 43.17 ± 13.34 –25.84 .02*

Tibialis anterior (TA) Right 84.92 ± 26.92 78.32 ± 13.83 –7.77 .440

Left 70.80 ± 24.36 80.76 ± 22.99 14.05 .400

Asterisks (*) indicate a significant difference (p < 0 .05). First motion = The median frequency of the first movement during ESL fatigue intervention; Last motion = The median frequency of the last movement during ESL fatigue intervention.

3.2. Field-goal percentage

Field-goal percentage dropped from 72.50 ± 18.15% before ESL fatigue intervention to 59.17 ± 15.64% after ESL fatigue (p = 0.031).

3.3. The lowest point of the CoM (Min-CoM)

No difference in the position of the Min-CoM was observed before versus after fatiguing the lower back muscles (before: 0.62 ± 0.04 m; after: 0.65 ± 0.05 m, p = 0.052) during CMJ. However, during JSs the Min-CoM significantly increased from 0.79 ± 0.05 m to 0.81 ± 0.05 m after the ESL fatigue (p = 0.042, ES = –0.67) (Figure 3).

The lowest point of the CoM (Min-CoM) during CMJs and JSs after erector spinae lumbalis fatigue. CMJ= counter-movement jump; JS= jump shot
Figure 3 

The lowest point of the CoM (Min-CoM) during CMJs and JSs after erector spinae lumbalis fatigue. CMJ = counter-movement jump; JS = jump shot.

3.4. Angles of the Lower Extremity Joints When the Knee Joint Reached the Maximum Flexion Angle

3.4.1. Ankle Joint Angles When the Knee Joint Reached the Maximum Flexion Angle

After the ESL fatigue, there was no significant difference in ankle joint angles when the knee joint reached the maximum flexion angle (Table 3).

Table 3

Angles of ankle joints when the knee joint reached the maximum flexion angle.


CMJ JS


AXIAL LEG HOPPING LEG AXIAL LEG HOPPING LEG

Before fatigue 42.41 ± 6.83° 42.86 ± 4.85° 40.38 ± 8.20° 40.03 ± 6.88°

After fatigue 41.47 ± 6.82° 42.21 ± 6.45° 40.10 ± 8.46° 38.71 ± 7.34°

p value 0.143 0.376 0.703 0.064

Effect size 0.46 0.27 0.11 0.59

CMJ = counter-movement jump; JS = jump shot.

3.4.2. Maximal Knee Flexion Angle

During CMJ and JS, the maximal knee flexion angle of the hopping leg showed no differences before and after the ESL fatigue. During JS, the maximal knee flexion angle of the axial leg showed no differences before and after the ESL fatigue. However, during CMJ, after ESL fatigue, the maximal flexion angle of the knee of the axial leg significantly decreased (p = 0.043, ES = –0.66) (Table 4).

Table 4

The maximal knee flexion Angles.


CMJ JS


AXIAL LEG HOPPING LEG AXIAL LEG HOPPING LEG

Before fatigue –111.86 ± 9.55° –113.09 ± 9.67° –99.56 ± 11.69° –94.84 ± 11.99°

After fatigue –107.87 ± 9.87° –109.03 ± 10.55° –97.42 ± 10.59° –92.60 ± 10.36°

p value 0.043* 0.054 0.127 0.076

Effect size –0.66 –0.62 –0.48 –0.57

Asterisks (*) indicate a significant difference (p < 0.05). CMJ = counter-movement jump; JS = jump shot.

3.4.3. Hip Joint Angles When the Knee Joint Reached the Maximum Flexion Angle

After ESL fatigue, no significant differences were found in the hip joint angle when the knee joint reached the maximum flexion angle of the axial leg and the hopping leg during CMJs. However, during JS, the hip joint angle of the axial leg and of the hopping leg was smaller after ESL fatigue (pre: 62.55 ± 8.01º, post: 59.23 ± 8.40º; p < 0.001, ES = 1.77). (pre: 61.50 ± 8.91º. post: 58.59 ± 8.68º; p = 0.004, ES = 1.07; Figure 4).

Hip Joint angles when the knee joint reached the maximum flexion angle during CMJ and JS. Asterisks (*) indicate a significant difference (p < .05). CMJ= counter-movement jump; JS= jump shot
Figure 4 

Hip Joint angles when the knee joint reached the maximum flexion angle during CMJ and JS. Asterisks (*) indicate a significant difference (p < .05). CMJ = counter-movement jump; JS = jump shot.

3.5. Instantaneous angles of the lower extremity joints during take-off

At the moment of take-off during CMJs and JSs, there were no differences in angles of lower extremity joints before and after ESL fatigue (Table 5).

Table 5

Angles of lower extremity joints at take-off.


BEFORE FATIGUE AFTER FATIGUE P VALUE EFFECT SIZE


AXIAL LEG HOPPING LEG AXIAL LEG HOPPING LEG

Hip joint CMJ 13.24 ± 4.86° 15.50 ± 5.31° 12.00 ± 4.78° 14.16 ± 3.89° A:0.225H:0.119 A:0.37H:0.49

JS 18.62 ± 6.15° 15.43 ± 5.06° 17.93 ± 6.33° 16.18 ± 7.11° A:0.505H:0.520 A:0.20H:-0.19

Knee joint CMJ –3.75 ± 4.97° –4.81 ± 5.21° –3.19 ± 4.51° –3.91 ± 4.42° A:0.580H:0.320 A:–0.16H:–0.30

JS –17.66 ± 7.33° –13.51 ± 7.69° –18.15 ± 7.60° –14.78 ± 7.81° A:0.607H:0.241 A:0.15H:0.36

Ankle joint CMJ –31.47 ± 5.10° –31.77 ± 3.43° –30.79 ± 4.71° –32.17 ± 3.30° A:0.382H:0.667 A:–0.26H:0.13

JS –27.27 ± 4.95° –29.77 ± 4.40° –27.03 ± 5.95° –30.00 ± 6.21° A:0.793H:0.836 A:–0.08H:0.06

Positive values indicate hip joint flexion, knee joint extension, and ankle joint in dorsal flexion. Negative values indicate hip joint extension, knee joint flexion, and ankle joint in plan-tar flexion. A = Axial leg; H = Hopping leg. CMJ = counter-movement jump; JS = jump shot.

3.6. Analyses of Landing Motion and Impact

3.6.1. Landing Angles of Lower Limb Joint

After the ESL muscle fatigue, the ankle joint landing angles (in plantarflexion) of the axial leg and the hopping leg were significantly increased during CMJ(p = 0.044, ES = 0.66; p = 0.005, ES = 1.02). During JS, after the ESL muscle fatigue, the plantarflexion angle of ankle joint of the hopping leg significantly increased (p = 0.037, ES = 0.68). During CMJ, at landing, after fatigue, the flexion angles of the knee joint of the hopping leg decreased (p = 0.046, ES = –0.65). For CMJ and JS, at landing, the hip joints angles showed no differences after the ESL fatigue (Table 6).

Table 6

Angles of lower extremity joints at landing.


BEFORE FATIGUE AFTER FATIGUE P VALUE EFFECT SIZE


AXIAL LEG HOPPING LEG AXIAL LEG HOPPING LEG

Hip joint CMJ 26.06 ± 6.98° 26.32 ± 6.05° 25.74 ± 4.62° 24.50 ± 5.94° A:0.879H:0.353 A:0.04H:0.28

JS 21.19 ± 4.70° 14.00 ± 6.99° 20.73 ± 4.40° 14.29 ± 6.99° A:0.518H:0.666 A:0.19H:-0.13

Knee joint CMJ –19.03 ± 5.75° –20.05 ± 6.34° –18.02 ± 5.29° –16.20 ± 5.33° A:0.500H:0.046* A:-0.20H:0.65

JS –16.83 ± 4.47° –15.15 ± 5.48° –17.68 ± 4.95° –14.79 ± 6.06° A:0.363H:0.663 A:0.27H:-0.13

Ankle joint CMJ –20.51 ± 5.82° –22.92 ± 5.30° –25.01 ± 4.14° –28.59 ± 5.69° A:0.044*H:0.005* A:0.66H:1.02

JS –27.97 ± 4.71° –29.47 ± 4.67° –29.14 ± 5.21° –31.73 ± 5.24° A:0.164H:0.037* A:0.43H:0.68

Asterisks (*) indicate a significant difference (p < .05) compared with joint angles before ESL fatigue. Positive values indicate hip joint flexion, knee joint extension, and ankle joint in dorsal flexion. Negative values indicate hip joint extension, knee joint flexion, and ankle joint in plan-tar flexion. A = Axial leg; H = Hopping leg. CMJ = counter-movement jump; JS = jump shot.

3.6.2. Contribution Ratio of Each Leg at Landing

During CMJ, whether ESL muscle fatigue or not, the contribution ratio of both legs was no significant difference and very closely (before fatigue: axial leg: hopping leg = 48.7:51.3; after fatigue: axial leg: hopping leg = 50.6:49.4). During JS, in the pretest, the landing supported much more by the axial leg (61.3:38.7; p < 0.05). However, after ESL muscle fatigue, there was no significant difference in the contributions ratio of the two legs (56.7:43.3) (Table 7).

Table 7

Contribution of each leg at landing (%).


CMJ JS


AXIAL LEG HOPPING LEG AXIAL LEG HOPPING LEG

Before fatigue 48.7 51.3 61.3 38.7*

After fatigue 50.6 49.4 56.7 43.3

Asterisks (*) indicate a significant difference (p < .05) compared with the contribution of the axial leg.

4. Discussion

The aim of the present study was to examine the influence of fatigue in the ESL on JS performance, CMJ movement patterns, and landing impact. Results showed that Field-goal percentage dropped significantly after ESL fatigue for the collegiate basketball players. During JS, after ESL muscle fatigue, lowest point of CoM is significantly increased and bilateral hip flexion angles when the knee reached the maximum flexion significantly decreased. During CMJ, after ESL muscle fatigue, bilateral ankle plantar flexion angle increased, and knee flexion angles of the hopping leg decreased significantly when landing. During JS, after ESL fatigue, ankle plantar flexion angle increased for the hopping leg. And during JS at landing, the contribution ratio of their feet changed after low back muscles fatigue. Additionally, the muscle was at fatigue when the median frequency decreased more than 41.66% (Horita and Ishiko, 1987). As indicated by the results of this study, the median frequencies of the left and right ESL decreased more than 41.66% (the median frequency of left ESL decreased 45.39%, and that of the right ESL decreased 46.63%), indicating ESL fatigue after fatigue intervention. However, although the decreases in the median frequencies of other muscle groups (RF, BF) were significant, the changes did not indicate fatigue according to the above-mentioned criteria (Horita and Ishiko, 1987). Besides, during the ESL fatigue intervention, the average EMG amplitude of ESL first increased and then decreased. Such a result may be attributed to the fatigue response at the beginning of the training, which increased the activation of the ESL. Therefore, Roman chair intervention in the present study could fatigue ESL without exhausting other lower extremity muscle groups (i.e., BF, RG, RA, RF and TA).

After fatigue, during JS, athletes had a significant decrease in bilateral hip flexion angles when the knee joint reached the maximum flexion angle in the present study. We found that the Min-CoM increased significantly during JSs after ESL fatigue, the hip joint angle of both legs decreased significantly, and there were no significant changes in the knee and ankle joints. It was presumed that the median frequency of the rectus femoris (responsible for part of the hip flexion movement) of both legs also decreased significantly after ESL fatigue, which further probably affected the hip joint angle during the jump. Hip joint flexion decreasing significantly showed that the athletes may not be able to reach the expected lowest CoM position and cause to reduce stability phase after ESL fatigue (Okazaki et al., 2015).

Zhang et al. found that reduced hip and knee stiffness after fatigue was associated with increased hip and knee range of motion (Zhang et al., 2018). Excessive joint motion tended to reduce joint stiffness. However, in this study, after ESL muscle fatigue, when the athlete landed, their knee flexion angles of the hopping leg were significantly reduced at CMJ. Also, the ankle joint landing angles (in plantarflexion) of the axial leg and the hopping leg were significantly increased. These angle changes after ESL fatigue indicated the athlete’s lower extremities were in a more stiff status when landing during the CMJ. However, stiff landing may cause excessive loading and injury of the lower limbs (Brizuela et al., 1997). In general, shock absorption during landing was usually achieved by bending the lower limb and using the midfoot to reduce local load and risk of injury (Struzik et al., 2014, Devita and Skelly, 1992). Nevertheless, in this study, when ESL fatigue was present, their knee flexion angles of the hopping leg was significantly reduced and the ankle plantarflexion angle was significantly increased. In comparison to a softer landing posture, ankle joint plantar flexors also contribute more to absorb more energy for a stiff landing posture. In addition, anticipation for landing enhances the musculotendinous structures in the foot, ankle, and other lower extremities before landing to immediately dissipation energy after landing impact (Devita and Skelly, 1992, Zhang et al., 2000). The subjects plantar flexed more when instructed to absorb the impact energy through their toes during more stiff landing (Self and Paine, 2001). Thus, after ES fatigue in our research the CMJ shows a more stiff landing and may requires more contribution from the ankle joint plantar flexors to resist the impact.

During JS, after ESL muscle fatigue, there were no significant differences in the angles of the hip and knee joints for either the axial or the hopping legs; however, after ESL fatigue, ankle plantar flexion angle increased for the hopping leg. Our result indicated that the athlete may use the ankle of the hopping leg as the main buffer joint after the lower back muscles fatigue. Therefore, there was a greater degree of plantar flexion to reduce the impact from landing.

The contributions of both feet at landing during CMJ before ESL fatigue were very close but a little bit toward the hopping leg (48.7:51.3), and after fatigue, there was a tendency for deviation toward the axial leg (50.6:49.4). During JS at landing, before fatigue, the contribution of both legs was deviated toward the axial leg, after fatigue, it deviated toward the hopping leg and a small difference in both feet which showing the destruction of the asymmetric character of JS. The axial leg served as the supporting leg closer to the trunk so that it absorbed a greater impact at landing because the body was kept stable and straight when performing JSs. When the ESL fatigue, the control in performing JS was changed. The body leaned towards the hopping leg and may reduce field-goal percentage during JS. Although it is logical that CMJ would be more symmetric than JS before or after core muscle fatigue, our study was also consistent with this trend. Previous studies have indicated that individual nature of asymmetries in jumping. The inter-limb asymmetries may influence the athlete’s performance (Bishop et al., 2021, Filip and Nejc, 2020) or may be not detrimental to sport performance (Dos’Santos et al., 2017). Larger asymmetries are associated with reduced jump performance (Bishop et al., 2021). However, inter-limb asymmetry appear to be more easily quantified by unilateral tasks (e.g., single-leg CMJ) (Bishop et al., 2021). From our data, before ESL fatigue, the landing supported much more by the axial leg significantly, and after ESL muscle fatigue, there was no difference in the contributions of the two legs. Our findings are considered within this context, JS may be a more functional action characterized by basketball players’ demands and may need to be included to assess asymmetries.

Knudson et al. (Knudson, 1993) identified the vertical jump as one of the biomechanical factors influencing field goal percentage. Decreased field-goal percentage possibly due to the athlete’s inability to achieve the desired min-CoM position. It was presumed that they were not utilizing their lower extremity as effectively to generate propulsive force during a jump shot. The stiffness of the knee and hip joints during landing was not sufficient to adjust the magnitude of the impact forces, joint loading and energy dissipation by adjusting the leg geometry, joint torque or stiffness and energy dissipation (Yeow et al., 2011, Rowley and Richards, 2015). Some researchers had observed greater GRF peaks after fatigue and a more upright landing posture (Cortes et al., 2014, Brazen et al., 2010). Those will be a risk factors for ACL ligament injury. Several studies had shown that neuromuscular fatigue can affect landing strategies in the lower limbs harmfully (Murdock and Hubley-Kozey, 2012, Madigan and Pidcoe, 2003).

The results of this study showed that the temporary fatigue of the ESL will first affect the pre-jump angles of bilateral hips during JS and may not be able to reach to the expected lowest CoM position and cause drop field-goal percentage after ESL fatigue. ESL fatigue also results in the increase of ankle plantarflexion angles and change of load ratio of both legs during landing when performing JS. The impact of trunk extensor muscle fatigue on movement, posture control, even on athletic performance should be taken into consideration during training or competition. Therefore, paying attention to avoid ESL muscle failure and giving enough recovery time were recommended.

5. Limitations

Firstly, only back core muscle fatigue intervention was performed in the current study. Muscle fatigue was relieved with time. If both abdominal and back core muscle training sessions were performed, one of the muscle groups could be restored during the process. Hence, fatigue of abdominal core muscles could not be tested together with the fatigue of back muscles. The ESL fatigue protocol was used in this study that might be considered as a limitation for the practical relevance of the finding. Second, regarding both abdominal and back core muscle training sessions the instrumentation, the two force plates were fixed at designated spots, and the distance between the plates could not be adjusted. Therefore, the subjects might have had to slightly change the distance between their feet to step on the plates, which might result in postures that were different from their actual landing postures. Third, the subjects in this study were all male, so the results cannot be directly applied to female athletes.

6. Conclusions

To our knowledge, our study group proposed repeated trunk extension exercise to make the trunk extensor fatigue. An objective way – EMG was used to detect muscle fatigue status as a novel way of quantifying and detecting back muscle fatigue in athletes. Temporary erector spinae lumbalis fatigue decreases JS field-goal percent of athletes and causes a change in the landing strategy. Due to erector spinae lumbalis fatigue, the basketball players increase ankle plantarflexion angles of the hopping leg and change of load ratio of both legs during landing when performing JS. We encourage practitioners to avoid over-load training enhancing core muscles fatigue and adequate rest is needed be-fore basketball competitions.

Ethics and Consent

The study was conducted according to the guidelines of the Declaration of Helsinki.

Acknowledgements

The authors would like to thank all those who contributed to this study.

Competing Interests

The authors have no competing interests to declare.

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