Effect of running-induced fatigue on lower limb mechanics in novice runners

Abstract

BACKGROUND:

Running-induced fatigue has received much attention in recent years. However, very few studies have investigated the effect of fatigue on lower limb biomechanics in three planes.

OBJECTIVE:

This study was designed to investigate biomechanical changes in the lower limb in three planes following running-induced fatigue.

METHODS:

Fifteen male novice runners were included in the study and performed three running trails pre- and post-fatigue. Wilcoxon signed-rank tests or paired-sample $t$ tests were used to analyze the data.

RESULTS:

Lower limb biomechanics significantly changed, especially kinetic parameters, when fatigue occurred. The peak ankle dorsiflexion angle and range of motion of the knee joint in the frontal plane increased. As for kinetic parameters, in the ankle joint, the peak external rotation moment, peak abduction power and peak internal rotation power increased. In the knee joint, the peak abduction and external rotation moment, peak flexion power, peak adduction and abduction power also increased. In the hip joint, the peak flexion moment was decreased, peak adduction and abduction moment, peak external rotation power, peak adduction and abduction power moment were increased.

CONCLUSION:

The findings of this study may contribute to our understanding of the impact of fatigue and provide some helpful information to prevent related injuries.

Keywords

Running-induced fatigue joint moment joint power running injury

1. Introduction

The benefits of physical activity have been widely acknowledged, and there have been increases in the number of people who participate in exercises. Recreational running is an easy and cost-effective method for individuals to keep fit and healthy. Recreational running also appeals to a vast number of people as a recreational pastime. Because of its popularity, running-related injuries have increased, especially in novice runners [1, 2]. Fatigue can be a contributing factor to an increase in running-related injuries. Fatigue can modify the running style of runners, and decrease impact peak and the loading rate of ground reaction forces (GRF), which are associated with running-related injuries [3]. Research has established that during long-distance running, the mean power frequency (MPF) of the tibialis anterior decreased significantly while the MPF of the gastrocnemius increased. Furthermore, findings revealed that the shank shock acceleration increased. This suggests that the loading balance on the tibia might be damaged which may lead to overuse injuries [4]. When fatigue occurs, shank shock acceleration steadily increases, and electromyogram measures (EMG) of the quadriceps and gastrocnemius muscles revealed that they were not related to fatigue. As a result, muscular fatigue may cause the human musculoskeletal system to become less able to manage a heel strike during running performance [5].

The magnitude and etiology of fatigue can be influenced by different types of exercises. During treadmill running, the hip and knee joint range of motion (ROM) increased while ankle stiffness decreased, to maintain similar impact forces [6]. Fatigue caused by five-hour hill running changed the running mechanics of vertical GRF, vertical stiffness and center of mass oscillating amplitude. However, the amplitude of these changes was lower than those observed after an ultramarathon [7].

Fischer et al. [8] used 60 s of countermovement jumps as a fatigue protocol to examine changes in running mechanics. The fatigue observed caused runners to adjust their running mechanics, with no change in vertical stiffness. Additional fatigue protocols consisting of sets of 10 bilateral squats (90 ${}^{\circ}$ knee flexion), two bilateral maximal effort vertical jumps and 20 steps (31 cm high stair) have been widely used to investigate the biomechanical changes of single-leg vertical jump pre- and post-fatigue. Following the onset of fatigue, trunk flexion increased but peak knee flexion decreased, which may result in a decrease in the stress on the anterior cruciate ligament (ACL) [9]. When single-leg landing after fatigue, knee and ankle flexion angles increased at the initial contact, and peak GRF as well as stabilizing time after landing were greater than those before fatigue [10]. Fatigue also effected peak foot abduction and peak rectus femoris activity [11], and increased dynamic loading of the human musculoskeletal system [12].

Running-induced fatigue has increased research interest, and significant increases in lower limb joint angles were found when fatigue occurred [13]. Compared to running over ground, running on a treadmill was found to increase contact time and reduce peak pressure [14]. Furthermore, regardless of whether the lower limb was dominant or not, fatigue occurred at the same rate [15]. Running experience has been observed to be associated with responses to fatigue [16]. Compared to novice sprinters, experienced sprinters showed a greater ability to maintain limb mechanics when fatigue occurred.

Many studies have focused on changes in lower limb mechanics induced by fatigue. However, little research has investigated the kinematics and kinetics of lower extremity fatigue in three planes. The aim of this study was to investigate biomechanical changes in the lower limb, namely the joint angle, joint angle velocity, joint moment and joint power when running-induced fatigue occurred. It was hypothesized that lower extremity biomechanics changed following fatigue, especially kinetic parameters. To be precise, joint moments and powers were larger under the fatigue condition.

2. Materials and methods

2.1 Participants

Fifteen male novice runners (mean age 23.8 $\pm$ 0.8 years, height 1.76 $\pm$ 2.71 m, weight 72.2 $\pm$ 5.94 kg, foot length 255 $\pm$ 0.71 mm) participated in the study. Novice runners were defined as runners who ran less than two-three times a week and ran less than 10 km per trail. All subjects were rear foot strikers free of lower limb injuries, surgeries or neuromuscular diseases within six months before data collection. Prior to the experiment, participants were informed of the test procedures and requirements. All subjects signed informed consent forms before data collection. The study was approved by the Human Ethics Committee of Ningbo University.

2.2 Experimental protocol

The experimental protocol consisted of three phases including pre-fatigue, fatigue protocol and post-fatigue. During the experiment, participants were given the same shoes to reduce error. Kinematic and kinetic data were synchronously collected pre- and post-fatigue. Eight infrared Vicon motion capture systems (Oxford metric Ltd., Oxford, UK) were used to capture kinematic date with a sampling frequency of 200 Hz. Based on a previous study, 21 reflective markers and six rigid marker clusters were attached to the lower limbs of participants [17]. Reflective markers were placed bilaterally over anatomical landmarks, including the anterior superior iliac spines, iliac crests, greater trochanters, lateral and medial femoral epicondyles, lateral and medial malleolus, distal interphalangeal joint of the second toe, the first and fifth metatarsal heads. The last single reflective marker was attached to the joint space between the fifth lumbar and the first sacral spinous processes. Six marker clusters were attached bilaterally to the thigh, leg and heel of the shoes by adhesive tape. All reflective markers were applied by an experienced researcher. Kinetic date was collected using a Kistler Force Platform (Model9281B, Winterthur, Switzerland) with a sampling frequency of 1000 Hz. Prior to the data collection, the force platform was zero-leveled. In order to ensure repeatability between conditions, the reflective marker attachment sites were marked using a marking pen. Subjects performed running at a self-selected speed along a 20 m runway in the lab with their dominant foot striking the force platform. The dominant limb was defined as the preferred leg used to kick a ball. Abnormal conditions such unnatural running postures were excluded from the data analysis, and a total of three sets of successful and reliable data were collected from each subject.

2.3 Running-induced fatigue protocol

Following data collection from the three successful trials on the dominant limb, participants were asked to perform a running-induced fatigue protocol based on previous studies [18, 19]. Throughout the protocol, subjects used the 15-point Borg scale to rate perceived exertion, and the heart rate was monitored throughout the trial (Polar H10, Finland). At the onset of the exercise, participants walked on a treadmill at a speed of six kilometers per hour. The speed of the treadmill increased by 1 km/h every 2 minutes, which facilitated the progress of walking into running. The subjects graded 13 as somewhat hard on the Borg scale. Once this intensity was reached, the subjects maintained the same speed. When the subjects graded 17 (very hard) or reached 90% of the maximum heart rate, they continued running for another two minutes until volitional exhaustion. The maximum heart rate was evaluated as 220 – age. [20].

2.4 Data processing

Experimental data from the three trials on the dominant extremity for each subject during the stance phase were processed using Visual3D software (version 3.26, C-Motion Inc., Germantown, MD, USA). The trajectories of the markers and force platform signals were filtered by a low-pass filter with a cut-off frequency of 10 Hz.

The kinematic variables of interest were: (1) peak joint angles of the ankle, knee and hip joints, (2) joints range of motion, (3) peak joint velocity of the ankle, knee and hip joints; kinetic variables of interest included: (1) peak joint moment of the ankle, knee and hip joints, (2) peak joint power of the ankle, knee and hip joints. All kinematic and kinetic values were obtained during the stance phase of the dominant limb during running at a self-selected speed. Joint angles and velocities were calculated in relation to the distal segment movement relative to the proximal segment. Joint moment and power were normalized. The signs used in this study indicate the direction of the joint movement, which are presented in Table 1.

Table 1
Sign conventions used for lower limbs

Joints	Sagittal	Frontal	Horizontal
Ankle	Dorsiflexion: $+$	Adduction: $+$	Internal rotation: $+$
	Plantar flexion: $-$	Abduction: $-$	External rotation: $-$
Knee	Extension: $+$	Adduction: $+$	Internal rotation: $+$
	Flexion: $-$	Abduction: $-$	External rotation: $-$
Hip	Flexion: $+$	Adduction: $+$	Internal rotation: $+$
	Extension: $-$	Abduction: $-$	External rotation: $-$

Shapiro-Wilk tests were carried out to examine whether the data were normally distributed. Many of these parameters did not obey normal distribution. Wilcoxon signed-rank tests, therefore, were used to assess the differences in parameters between pre-fatigue and post-fatigue. Paired sample $t$ -tests were used if the parameters were normally distributed. All values were expressed as means, standard deviations and medians. Statistical analysis was conducted using SPSS25.0 (SPSS, Chicago, IL, USA) with an alpha level set as 0.05. Effect sizes (ES) using Cohen’s d were also calculated by G*Power, and 0.2, 0.5, 0.8 were critical values of the three classes which were small, medium and large [21].

3. Results

Lower limb joint angles during the stance phase between pre- and post-fatigue are presented in Fig. 1 and Table 3. Most values did not significantly change when fatigue occurred. In the sagittal plane, the maximum ankle angle of pre-fatigue was 3.83 ${}^{\circ}$ smaller than that of post-fatigue ( $P=$ 0.041, ES $=$ 0.65). In the frontal plane, range of motion (ROM) of the knee before and after fatigue was 2.99 ${}^{\circ}$ and 6.16 ${}^{\circ}$ , respectively, which was significantly different ( $P=$ 0.011, ES $=$ 0.75).

Continuous joint velocities of the lower limb are shown in Fig. 2, and peak values are presented in Table 3. In the frontal plane, the maximum ankle angular velocity of pre-fatigue was significantly smaller than that of post-fatigue ( $P=$ 0.02, ES $=$ 0.43). Peak knee angular velocities were significantly smaller following fatigue (maximum: $P=$ 0.017, ES $=$ 0.68; minimum: $P=$ 0.004, ES $=$ 0.80).

Continuous joint moments of the lower limb are shown in Fig. 3, and peak values are presented in Table 4. In the sagittal plane, the maximum moment of the hip joint before fatigue was significantly larger when compared to post-fatigue ( $P=$ 0.001, ES $=$ 1.24). In the frontal plane, the minimal knee moment during the stance phase was $-$ 0.13 Nm/kg (pre-fatigue) and $-$ 0.20 Nm/kg (post-fatigue), which was significantly different ( $P=$ 0.012, ES $=$ 0.78). Furthermore, the peak moment values of the hip joint were significantly smaller than those measured under fatigue conditions (maximum: $P=$ 0.017, ES $=$ 0.53; minimum: $P=$ 0.001, ES $=$ 1.16). In the horizontal plane, the minimal ankle moment before fatigue was $-$ 0.04 Nm/kg (minus indicates planter flexion), which was significantly smaller than after fatigue ( $P=$ 0.027, ES $=$ 0.76). The minimal knee moment under pre-fatigue conditions was smaller compared to fatigue conditions ( $P=$ 0.027, ES $=$ 0.80).

Continuous joint powers of the lower limb are shown in Fig. 4, and peak values are presented in Table 5. In the sagittal plane, the minimal knee joint power before fatigue was significantly smaller than when fatigue was induced ( $P=$ 0.041, ES $=$ 0.52). In the frontal plane, the minimal ankle joint power was significantly smaller under pre-fatigue conditions ( $P=$ 0.015, ES $=$ 0.66). Peak power values of the knee

Table 2
Peak joint angles and ROM of pre-fatigue and post-fatigue during stance phase

Joint	Plane	Pre												Post
		Max				Min				ROM				Max				Min				ROM
		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.
Ankle ( ${}^{\circ}$ )	Sagittal	16.99	(3.41)	15.	48 ${}^{\ast}$	$-$ 11.76	(5.87)	$-$ 14.	44	28.75	(3.43)	28.	38	19.64	(4.68)	19.	30	$-$ 9.22	(5.81)	$-$ 8.	90	28.86	(3.67)	26.	83
	Frontal	0.52	(3.78)	0.	17	$-$ 12.20	(3.31)	$-$ 13.	13	12.73	(1.71)	12.	93	1.18	(5.63)	2.	80	$-$ 13.15	(5.23)	$-$ 11.	66	14.33	(2.14)	13.	41
	Horizontal	4.08	(3.27)	3.	11	$-$ 7.26	(3.40)	$-$ 7.	43	11.34	(5.72)	10.	01	5.04	(10.01)	3.	45	$-$ 7.47	(6.02)	$-$ 6.	17	12.50	(7.55)	11.	34
Knee ( ${}^{\circ}$ )	Sagittal	$-$ 17.08	(3.87)	$-$ 17.	19	$-$ 39.25	(4.68)	$-$ 40.	58	22.17	(3.51)	22.	24	$-$ 18.33	(6.49)	$-$ 18.	78	$-$ 39.87	(5.24)	$-$ 39.	01	21.54	(3.11)	22.	00
	Frontal	4.23	(2.69)	5.	02	0.51	(3.48)	2.	15	3.72	(2.29)	2.	99 ${}^{\ast}$	7.01	(8.50)	6.	73	0.88	(7.84)	0.	73	6.13	(3.93)	6.	16
	Horizontal	9.29	(6.14)	11.	26	$-$ 1.08	(6.84)	$-$ 1.	99	10.37	(2.67)	10.	68	7.51	(21.06)	12.	31	$-$ 3.30	(23.57)	4.	64	10.81	(3.39)	10.	59
Hip ( ${}^{\circ}$ )	Sagittal	23.15	(5.97)	21.	25	$-$ 7.48	(4.68)	$-$ 8.	56	30.63	(2.49)	31.	39	23.61	(5.95)	24.	96	$-$ 7.83	(5.26)	$-$ 6.	32	31.44	(3.67)	31.	38
	Frontal	8.17	(2.19)	7.	86	$-$ 1.23	(2.14)	$-$ 1.	29	9.40	(2.24)	9.	46	10.42	(4.90)	8.	48	$-$ 0.24	(4.5)	$-$ 3.	05	10.66	(1.47)	11.	05
	Horizontal	4.45	(2.36)	3.	72	$-$ 2.79	(3.20)	$-$ 3.	93	7.24	(1.98)	7.	31	6.49	(13.92)	4.	12	$-$ 1.07	(15.62)	$-$ 3.	39	7.57	(2.07)	7.	29

Table 3

Peak joint velocities of pre-fatigue and post-fatigue during stance phase

Joint	Plane	Pre								Post
		Max				Min				Max				Min
		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.		Mean (SD)		Med.
Ankle ( ${}^{\circ}$ /s)	Sagittal	200.88	(37.62)	192.	57	$-$ 291.04	(42.04)	$-$ 295.	55	198.63	(27.90)	182.	17	$-$ 282.26	(39.78)	$-$ 273.	77
	Frontal	166.57	(59.75)	168.	65 ${}^{\ast}$	$-$ 88.96	(33.01)	$-$ 72.	80	193.39	(65.89)	177.	02	$-$ 104.31	(43.35)	$-$ 111.	553
	Horizontal	93.80	(35.04)	85.	29	$-$ 126.21	(59.42)	$-$ 121.	60	86.95	(38.69)	86.	77	$-$ 120.84	(32.65)	$-$ 114.	74
Knee ( ${}^{\circ}$ /s)	Sagittal	129.35	(41.10)	146.	85	$-$ 280.34	(55.11)	$-$ 260.	07	147.01	(21.99)	145.	93	$-$ 265.38	(38.51)	$-$ 259.	65
	Frontal	45.06	(26.83)	48.	86 ${}^{\ast}$	$-$ 58.84	(31.19)	$-$ 46.	35 ${}^{\ast}$	71.04	(46.86)	52.	19 ${}^{\ast}$	$-$ 90.10	(45.95)	$-$ 67.	75 ${}^{\ast}$
	Horizontal	128.47	(45.42)	111.	35	$-$ 97.37	(35.96)	$-$ 94.	54	127.38	(32.78)	127.	80	$-$ 86.73	(11.61)	$-$ 87.	08
Hip ( ${}^{\circ}$ /s)	Sagittal	10.93	(29.21)	0.	75	$-$ 183.83	(33.35)	$-$ 176.	81	3.58	(7.97)	0.	57	$-$ 185.10	(30.89)	$-$ 176.	05
	Frontal	71.54	(27.30)	74.	61	$-$ 59.66	(27.35)	$-$ 56.	13	74.07	(15.45)	73.	15	$-$ 63.49	(11.57)	$-$ 66.	74
	Horizontal	88.89	(51.07)	82.	38	$-$ 30.27	(29.67)	$-$ 24.	59	74.72	(24.72)	78.	63	$-$ 47.40	(30.31)	$-$ 52.	50

Table 4

Peak joint moments of pre-fatigue and post-fatigue during stance phase

Joint	Plane	Pre				Post
		Max		Min		Max		Min
		Mean (SD)	Med.	Mean (SD)	Med.	Mean (SD)	Med.	Mean (SD)	Med.
Ankle	Sagittal	0.09 (0.11)	0.04	$-$ 0.51 (0.59)	$-$ 0.54	0.11 (0.12)	0.09	$-$ 0.85 (0.73)	$-$ 0.99
(Nm/kg)	Frontal	0.05 (0.09)	0.03	$-$ 0.03 (0.04)	$-$ 0.01	0.08 (0.11)	0.01	$-$ 0.04 (0.04)	$-$ 0.02
	Horizontal	0.01 (0.01)	0.01	$-$ 0.05 (0.06)	$-$ 0.04 ${}^{\ast}$	0.02 (0.02)	0.01	$-$ 0.14 (0.15)	$-$ 0.06
Knee	Sagittal	0.23 (0.19)	0.16	$-$ 0.70 (0.62)	$-$ 0.68	0.38 (0.34)	0.36	$-$ 0.98 (0.60)	$-$ 1.3
(Nm/kg)	Frontal	0.06 (0.05)	0.04	$-$ 0.15 (0.14)	$-$ 0.13 ${}^{\ast}$	0.06 (0.03)	0.05	$-$ 0.29 (0.22)	$-$ 0.20
	Horizontal	0.01 (0.02)	0.01	$-$ 0.04 (0.05)	$-$ 0.02 ${}^{\ast}$	0.02 (0.02)	0.03	$-$ 0.11 (0.11)	$-$ 0.08
Hip	Sagittal	0.75 (0.18)	0.73 ${}^{\ast}$	$-$ 1.73 (0.54)	$-$ 1.62	0.56 (0.11)	0.56	$-$ 1.72 (0.41)	$-$ 1.73
(Nm/kg)	Frontal	0.25 (0.18)	0.19 ${}^{\ast}$	$-$ 0.33 (0.27)	$-$ 0.24 ${}^{\ast}$	0.39 (0.31)	0.21	$-$ 0.66 (0.30)	$-$ 0.55
	Horizontal	0.09 (0.08)	0.06	$-$ 0.05 (0.03)	$-$ 0.04	0.15 (0.11)	0.16	$-$ 0.05 (0.04)	$-$ 0.03

Pre: pre-fatigue; post: post-fatigue; Med: median; SD: standard deviation. ${}^{\ast}$ Indicates a significant difference between pre- and post-fatigue.

Table 5

Peak joint powers of pre-fatigue and post-fatigue during stance phase

Joint	Plane	Pre				Post
		Max		Min		Max		Min
		Mean (SD)	Med.	Mean (SD)	Med.	Mean (SD)	Med.	Mean (SD)	Med.
Ankle	Sagittal	2.30 (2.83)	1.67	$-$ 0.79 (0.90)	$-$ 0.83	3.54 (3.20)	3.40	$-$ 1.41 (1.52)	$-$ 1.38
(W/kg)	Frontal	0.04 (0.08)	0.02	$-$ 0.04 (0.06)	$-$ 0.01 ${}^{\ast}$	0.09 (0.13)	0.03	$-$ 0.08 (0.07)	$-$ 0.06
	Horizontal	0.01 (0.01)	0.01	$-$ 0.07 (0.10)	$-$ 0.03 ${}^{\ast}$	0.04 (0.05)	0.02	$-$ 0.15 (0.21)	$-$ 0.09
Knee	Sagittal	0.50 (0.34)	0.49	$-$ 1.50 (1.80)	0.65 ${}^{\ast}$	0.58 (0.32)	0.63	$-$ 2.49 (2.01)	$-$ 2.63
(W/kg)	Frontal	0.06 (0.08)	0.04 ${}^{\ast}$	$-$ 0.06 (0.09)	$-$ 0.02 ${}^{\ast}$	0.19 (0.30)	0.06	$-$ 0.33 (0.49)	$-$ 0.20
	Horizontal	0.06 (0.08)	0.03	$-$ 0.02 (0.01)	$-$ 0.02	0.10 (0.10)	0.09	$-$ 0.03 (0.03)	$-$ 0.01
Hip	Sagittal	2.37 (2.41)	1.39	$-$ 0.99 (0.53)	$-$ 1.00	2.82 (2.37)	2.67	$-$ 0.91 (0.39)	$-$ 0.79
(W/kg)	Frontal	0.51 (0.59)	0.28 ${}^{\ast}$	$-$ 0.18 (0.18)	$-$ 0.14 ${}^{\ast}$	1.06 (1.14)	0.67	$-$ 0.34 (0.17)	$-$ 0.36
	Horizontal	0.08 (0.08)	0.03 ${}^{\ast}$	$-$ 0.08 (0.13)	$-$ 0.05	0.17 (0.17)	0.09	$-$ 0.08 (0.08)	$-$ 0.05

Pre: pre-fatigue; post: post-fatigue; Med: median; SD: standard deviation. ${}^{\ast}$ Indicates a significant difference between pre- and post-fatigue.

Figure 1.

Successive joint angle curves between pre- (red lines) and post-fatigue (blue lines) during stance phase. Solid lines indicate mean values over stance phase and shaded areas indicate standard deviations. Pre: pre-fatigue, post: post-fatigue.

Figure 2.

Successive joint angle velocity curves between pre- (red lines) and post-fatigue (blue lines) during stance phase. Solid lines indicate mean values over stance phase and shaded areas indicate standard deviations. Pre: pre-fatigue, post: post-fatigue.

Figure 3.

Successive joint moment curves between pre- (red lines) and post-fatigue (blue lines) during stance phase. Solid lines indicate mean values over stance phase and shaded areas indicate standard deviations. Pre: pre-fatigue, post: post-fatigue.

Figure 4.

joint before fatigue were significantly smaller compared to post-fatigue conditions (maximum: $P=$ 0.017, ES $=$ 0.58; minimum: $P=$ 0.004, ES $=$ 0.75). The same results were observed for the hip joint (maximum: $P=$ 0.002, ES $=$ 0.61; minimum: $P=$ 0.041, ES $=$ 0.87). In the horizontal plane, the maximum power values of the ankle and hip joints before fatigue were significantly smaller than those under fatigue conditions (ankle: $P=$ 0.002, ES $=$ 0.78; hip: $P=$ 0.009, ES $=$ 0.68).

4. Discussion

This study was carried out to investigate the effect of fatigue on lower limb kinematics and kinetics during the stance phase of running in novice runners. We hypothesized that fatigue influenced the biomechanics of the lower limbs, especially kinetic parameters, which was confirmed by our findings. Fatigue-induced changes in kinematics (Tables 3 and 3) occurred in the ankle and knee joints, whereas kinetic changes (Tables 4 and 5) occurred in all three joints.

In this study, the peak dorsiflexion angle of the ankle joint during the stance phase was larger following fatigue. In the frontal plane, the range of motion (ROM) of the knee joint before fatigue was smaller than that recorded in the fatigue condition. As for joint angular velocity, differences were observed in the frontal plane. The peak values of ankle adduction angular velocity, knee adduction and abduction angular velocity increased in the fatigued state. A decrease in hip flexion moments was observed when fatigue occurred. Also, hip adduction and abduction moments, knee adduction moments, knee external rotation moments as well as ankle external rotation moments decreased. Fatigue furthermore induced a joint power increase. In the ankle joint, the peak values of adduction and internal rotation power increased. The increase in joint power also occurred in the knee and hip joints.

As a result of the kinematic changes of the lower limbs under fatigue conditions, the ankle and knee joints, and especially the knee joint, should be emphasized. The kinematics of the hip joint did not change. At the ankle joint, the maximum ankle dorsiflexion angle was increased under the fatigue condition. After prolonged running, which induced central fatigue, the strength of the plantar flexor reduced [22]. Thus, we speculated that an imbalance existed between the dorsiflexor and plantar flexor muscles following fatigue. Besides, the fatigue of the plantar flexors and dorsiflexors may probably increase the amplitude of postural sway and makes the ankle joint more prone to injuries [23]. At the knee joint, the ROM in the frontal plane, as well as peak adduction and abduction angular velocity were increased from pre-fatigue to post-fatigue, which makes the knee joint more susceptible to injuries as well as the incidence of patellofemoral pain syndrome [24]. The knee adduction and abduction angles were related to anterior cruciate ligament rupture during landing tasks in females [25]. When fatigue occurred, the ROM of the knee in the frontal plane increased which means that the knee joint was more flexible in the frontal plane. Furthermore, the peak knee angular velocity in the frontal plane increased under the fatigue condition. Therefore, the anterior cruciate ligament, as a structure that restricts joint motion, has a potentially higher risk for injury.

Fatigue can also change the lower limb kinetics during running performance, including ground reaction forces, joint moment and joint power [3, 26, 27, 28]. At the ankle joint, the peak external rotation moment, the peak abduction power and peak internal rotation power increased as fatigue set in. At the knee joint, the peak abduction and external rotation moment, the peak flexion power, the peak power values in the frontal plane were all increased under fatigued conditions. At the hip joint, the peak flexion moment, the peak moment values in the frontal plane were increased, and the peak power values in the frontal plane and peak internal rotation power were increased when fatigue occurred. These findings are partially in line with previous studies [29]. Hip and knee joints play a vital part in the response to fatigue. The change in lower limb joint kinetics were related to lower limb muscles. Hip adductors and external rotators, to some extent, could prevent excessive femoral adduction and internal rotation [30]. Running-induced fatigue resulted in a decrease in lower limb muscular strength; therefore, lower limb moments and power were significantly changed, which resulted in a higher injury risk in the lower limb joints.

Some limitations in this study should be taken into consideration. First, only male novice runners were included, as a result findings should only apply to male populations [9]. Second, only peak values of lower limb joints were taken into consideration. Further investigations should focus on all continuous values during the stance phase or gait. Third, the self-selected running speed might change under fatigue condition, which might influence the results. Fourth, due to the limitation of equipment, we did not capture the lower limb biomechanics immediately, which may have resulted in a few small errors.

5. Conclusion

This study analyzed the effect of running- induced fatigue on the biomechanics of the lower limb when running. Overall, the kinematics and kinetics of lower limb joints changed, including joint angles, joint angular velocities, joint moments and joint powers. No kinematic changes in the hip joint were found when fatigue occurred. Kinetics changed especially in the frontal plane. The findings of this study may contribute to the understanding of the impact of fatigue and provide some useful information to prevent related injuries.

Footnotes

Acknowledgments

This study was supported by National Natural Science Foundation of China (No. 81772423), and K. C. Wong Magna Fund in Ningbo University.

Conflict of interest

None to report.

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Effect of running-induced fatigue on lower limb mechanics in novice runners

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Materials and methods

2.1 Participants

2.2 Experimental protocol

2.3 Running-induced fatigue protocol

2.4 Data processing

Table 1 Sign conventions used for lower limbs

Table 2 Peak joint angles and ROM of pre-fatigue and post-fatigue during stance phase

5. Conclusion

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Sign conventions used for lower limbs

Table 2
Peak joint angles and ROM of pre-fatigue and post-fatigue during stance phase