Effects of the abdominal drawing-in maneuver on hamstring rotational activity and pelvic stability in females

Abstract

BACKGROUND:

The medial hamstring (MH) and lateral hamstring (LH) can be selectively trained through tibial internal and external rotation during prone knee flexion. However, no study has identified how a combined tibial rotation and lumbo-pelvic stability strategy influences MH and LH muscle activities.

OBJECTIVE:

To investigate the combined effects of tibial rotation and the abdominal drawing-in maneuver (ADIM) on MH and LH muscle activities as well as pelvic rotation during prone knee flexion.

METHODS:

Fifteen female volunteers performed prone knee flexion with tibial internal and external rotation, with and without the ADIM. Under each condition, MH and LH muscle activities were measured by surface electromyography (EMG), and the pelvic rotation angle by a smartphone inclinometer application.

RESULTS:

The results showed increased MH (without the ADIM: $p<$ 0.001, effect size ( $d$ ) $=$ 2.05; with the ADIM: $p<$ 0.001, $d=$ 1.71) and LH (without the ADIM: $p<$ 0.001, $d=$ 1.64; with the ADIM: $p=$ 0.001, $d=$ 1.58) muscle activities under internal and external tibial rotation, respectively. However, addition of the ADIM led to increased MH (internal tibial rotation: $p=$ 0.001, $d=$ 0.67; external tibial rotation: $p=$ 0.019, $d=$ 0.45) and LH (internal tibial rotation: $p=$ 0.003, $d=$ 0.79; external tibial rotation: $p<$ 0.001, $d=$ 1.05) muscle activities combined with reduced pelvic rotation (internal tibial rotation: $p<$ 0.001, $d=$ 3.45; external tibial rotation: $p<$ 0.001, $d=$ 3.01) during prone knee flexion.

CONCLUSIONS:

These findings suggest that the ADIM could be useful for reducing compensatory pelvic rotation and enhancing selective muscle activation in the MH and LH, according to the direction of tibial rotation, during prone knee flexion.

Keywords

Hamstring tibial rotation abdominal drawing in-maneuver pelvic rotation

1. Introduction

Medial hamstring (MH) and lateral hamstring (LH) activation imbalance is associated with medial knee osteoarthritis (OA) and anterior cruciate ligament (ACL) injury. Lynn and Costigan reported a decreased MH and LH hamstring activation ratio during walking in those with medial knee OA, which was a compensation strategy to overcome the increased knee varus moment [1]. Briem et al. demonstrated greater relative LH hamstring activation in an ACL injury group compared to a control group due to increased knee valgus, as an element of the ACL injury mechanism [2]. Thus, an effective strategy to enhance selective activation of the hamstring muscle is crucial to prevent and/or treat knee injuries.

Changing the position of the tibia can help to selectively activate the MH or LH muscles. Lynn and Costigan demonstrated that the MH/LH activation ratio significantly increases upon tibial internal rotation and decreases upon tibial external rotation during standard lower limb exercises [3]. Mohamed et al. reported that the maximum MH and LH muscle activities significantly increased upon the tibial internal and external rotations, respectively, during 70 ${}^{\circ}$ knee flexion in the prone position [4].

Hamstring muscle activities are affected by tibial rotation and lumbo-pelvic stability. Oh et al. demonstrated that a lumbo-pelvic stabilization strategy using the abdominal drawing-in maneuver (ADIM) increases hamstring activity during prone hip extension [5]. Park et al. also showed an increase in hamstring muscle activity under the ADIM condition compared with the non-ADIM condition during prone knee flexion in patients with chronic low back pain [6]. In addition, they observed significantly reduced pelvic rotation under the ADIM condition, suggesting that a lumbo-pelvic stabilization strategy using the ADIM could lead to increased hamstring muscle activation in the neutral pelvic position [6].

These findings indicate that hamstring muscle activity changes significantly according to the direction of tibial rotation and the lumbo-pelvic stabilization strategy. Although tibial rotation and lumbo-pelvic stabilization strategies are effective for increasing hamstring muscle activation when used separately, no study has investigated how the combination of these strategies influences hamstring muscle activation and pelvic rotation. Therefore, this study analyzed the combined effect of tibial rotation and ADIM on electromyography (EMG) activity in the MH and LH as well as pelvic rotation, during prone knee flexion. We hypothesized that ADIM would facilitate EMG activity of the MH and LH, and reduce pelvic rotation. Meanwhile, internal and external tibial rotation would increase MH and LH muscle activity, respectively, during prone knee flexion. Given the clinical significance of the hamstring muscles, exercise methods that can selectively enhance MH and LH activities will be useful options for clinicians planning hamstring strengthening exercise strategies.

2. Methods

2.1 Participants

Fifteen healthy female volunteers who could perform activities of daily living without pain participated in this study (age $=$ 33.7 $\pm$ 6.91 years; height $=$ 161.80 $\pm$ 4.42 cm; body weight $=$ 51.06 $\pm$ 3.77 kg). The exclusion criteria were (1) presence of pain in a low back and lower extremity; (2) existing diagnosis of a musculoskeletal disorder in the trunk and/or a lower extremity at the time of the experiment; and/or (3) a history of hamstring injury or knee ligament deficiency. Of the 15 participants, 11 had experienced childbirth. All participants provided written informed consent. The study protocol was approved by the Institutional Review Board of Inje University. Based on a large effect size ( $d=$ 0.8) [7, 8], power of 0.8, and significance level of 0.05, power analysis showed that at least 15 participants were required to detect differences in hamstring muscle activity during prone knee flexion according to with and without the ADIM.

Figure 1.

Prone knee flexion with tibial rotation under the non-ADIM (A) and ADIM (B) conditions. Abbreviation: ADIM, abdominal drawing-in maneuver.

2.2 Surface EMG and data processing

Surface EMG electrodes (Delsys Triagno Wireless EMG system; Delsys Inc., Boston, MA, USA) were placed on the participants’ muscles parallel to the muscle fiber direction. The skin was shaved and, cleaned, and two surface electrode pairs were placed on the semimembranosus/semitendinosus (MH) and biceps femoris (LH) muscles of the dominant leg [9]. The EMG signals were amplified and sampled at 2,000 Hz with a bandwidth of 20–450 Hz. The raw EMG data were analyzed based on the root mean square and a 125-ms interval. The MH electrodes were placed at the midpoint between the ischial tuberosity and medial femoral epicondyle. The LH electrodes were placed between the ischial tuberosity and lateral femoral epicondyle. The muscle bellies for electrode placement on the MH and LH were manually identified by palpation during submaximal contraction. For normalization, two trials of 5 s maximal voluntary isometric contraction (MVIC) of the knee flexor, using knee flexion with internal tibial rotation (for MH), or external tibial rotation (for LH), were performed. While in the prone position, the participants performed 30 ${}^{\circ}$ maximal knee flexion with maintenance of the volitional internal and external rotation of the tibia against manual resistance for the MH and LH, respectively. The first and last 1-s intervals of each MVIC trial were removed from the data, and the mean value of the middle 3-s interval of each MVIC trial was calculated to obtain steady-state results. The mean values of two MVIC trials for the MH and LH, respectively, were calculated to determine the final MVIC values of the MH and LH. The EMG data of the MH and LH during each prone knee flexion test were expressed as a percentage of the MVIC (%MVIC) for data analysis.

2.3 Smartphone-based measurement tool (SBMT)

Pelvic rotation in both the sagittal and transverse planes has been reported as a common compensatory movement during prone knee flexion [6, 10, 11]. Although 3D motion analysis has been used to measure kinematics of the pelvis [6, 10, 11], a previous study demonstrated that pelvic transverse rotation can be reliably measured using a smartphone inclinometer application [12]. Similarly, in this study, we measured the pelvic transverse rotation angle using a smartphone inclinometer application. For pelvic transverse rotation measurements, smartphone was connected to the smartphone holder of SBMT, an instrument containing a wooden frame that could hold the smartphone in a position where it can measure the transverse rotation angle of the pelvis. A previous study demonstrated excellent reliability in pelvic rotation measurement using the SMBT [12]. To measure pelvic rotation, the bottom horizontal bar of the SBMT was placed on both posterior superior iliac spines. An Android inclinometer application (clinometer level and slope finder; Plaincode Software Solutions, Stephanskirchen, Germany) was used to record the pelvic rotation angle during prone knee flexion. Before the SMBT measurements, the inclinometer application was calibrated by placing the SBMT on a flat surface. The absolute pelvic rotation angle was measured during each prone knee flexion task.

2.4 Procedure

Before performing prone knee flexion tasks, the participants stretched their hamstrings to prevent muscle strain [13]. The participants tilted their pelvises forward with a straight-back posture while placing one leg on a chair in the standing position [14]. Each 20–30-s stretch, was repeated three times [15]. The participants were allowed rest periods of 45 s between stretches.

2.4.1 Prone knee flexion without the ADIM

The participants were asked to assume a prone position on the treatment table, then actively flex the knee joint toward the buttocks as much as possible for each of two tibial rotation conditions (e.g., internal and external) (Fig. 1A). Under both conditions, an investigator manually rotated the tibia to the direction of internal or external rotation until firm resistance was encountered. Subsequently, the participants flexed their knees for 5 s under each tibial rotation condition.

Table 1
Muscle activities of the medial and lateral hamstring muscles and pelvic rotation angles during prone knee flexion

Measure	Without ADIM		With ADIM		$P$ (Partial eta squared)
	Tibial internal rotation	Tibial external rotation	Tibial internal rotation	Tibial external rotation	Inter-action	Bio-feedback	Tibial rotation
Medial hamstring	42.51 $\pm$ 11.74	20.59 $\pm$ 9.20	53.83 $\pm$ 19.21	25.19 $\pm$ 11.19	0.047 ${}^{\ast}$ (0.253)	$<$ 0.001 ${}^{\ast}$ (0.612)	$<$ 0.001 ${}^{\ast}$ (0.703)
(%MVIC)
Lateral hamstring	21.94 $\pm$ 10.03	40.95 $\pm$ 12.69	32.26 $\pm$ 14.87	54.59 $\pm$ 13.30	0.413 (0.048)	$<$ 0.001 ${}^{\ast}$ (0.792)	$<$ 0.001 ${}^{\ast}$ (0.651)
(%MVIC)
Pelvic rotation	2.00 $\pm$ 0.49	2.31 $\pm$ 0.67	0.53 $\pm$ 0.29	0.55 $\pm$ 0.27	0.131 (0.155)	$<$ 0.001 ${}^{\ast}$ (0.944)	0.059 (0.232)
angle ( ${}^{\circ}$ )

${}^{\ast}p<$ 0.05. Abbreviations: ADIM, abdominal drawing-in maneuver; %MVIC, percentage of maximal voluntary isometric contraction.

2.4.2 Prone knee flexion with the ADIM

A pressure biofeedback unit was placed between the treatment table and the participant’s lower abdomen, while the participant was situated in a prone position. The pressure biofeedback unit was inflated to 70 mmHg, and the participant drew in their lower abdomen to reach pressure of 60 mmHg. The participant then performed prone knee flexion while maintaining a pressure of 60 mmHg during prone knee flexion with tibial internal or external rotation, as in knee flexion without the ADIM (Fig. 1B). Pressure changes of $\pm$ 5 mmHg were permitted to allow changes due to breathing [16]. Test trials were performed after several practice trials to allow familiarization with the knee flexion with ADIM procedure.

Each prone knee flexion was repeated three times with a 1-min rest period between trials and a 5-min rest period between conditions. To minimize learning effects regarding the ADIM, prone knee flexion without the ADIM was performed first, followed by prone knee flexion with the ADIM. Tibial internal or external rotation was randomly applied in each prone knee flexion condition.

2.5 Statistical analyses

IBM SPSS Statistics (ver. 25.0; IBM Corp., Armonk, NY, USA) was used to analyze the MH and LH muscle activities and pelvic rotation angle. For analysis of EMG muscle activity across the exercise conditions, 2 $\times$ 2 (tibial position $\times$ ADIM condition) repeated-measures analysis of variance was used. If interactions or main effects were observed regarding tibial position and ADIM condition, post hoc analysis was conducted using Bonferroni correction with a significance level of $p<$ 0.05.

3. Results

The results of statistical analysis are summarized in Table 1. An interaction between ADIM condition and tibial rotation was found for the MH ( $F_{1,14}=$ 4.730, $p=$ 0.047) but not for the LH ( $F_{1,14}=$ 0.713, $p=$ 0.413). The main effects of tibial rotation (MH: $F_{1,14}=$ 33.210, $p<$ 0.001; LH: $F_{1,14}=$ 26.105, $p<$ 0.001) and ADIM condition (MH: $F_{1,14}=$ 22.072, $p<$ 0.001; LH: $F_{1,14}=$ 53.301, $p<$ 0.001) were significant for both the MH and LH.

Post hoc analysis showed that MH muscle activity (without ADIM: $p<$ 0.001, $d=$ 2.05, confidence interval [CI] $=$ 14.035–29.814; with ADIM: $p<$ 0.001, $d=$ 1.71, CI $=$ 16.946–40.336) was significantly greater under the internal tibial rotation condition than under the external tibial rotation condition, whereas LH muscle activity (without ADIM: $p<$ 0.001, $d=$ 1.64, CI $=$ 11.326–26.687; with ADIM: $p=$ 0.001, $d=$ 1.58, CI $=$ 11.051–33.607) was significantly greater under the external tibial rotation condition than under the internal tibial rotation condition.

When the ADIM was applied during knee flexion, greater muscle activities in both the MH (internal tibial rotation: $p=$ 0.001, $d=$ 0.67, CI $=$ 5.453–17.186; external tibial rotation: $p=$ 0.019, $d=$ 0.45, CI $=$ 0.869–8.337) and LH (internal tibial rotation: $p=$ 0.003, $d=$ 0.79, CI $=$ 4.101–16.536; external tibial rotation: $p<$ 0.001, $d=$ 1.05, CI $=$ 8.978–18.304) were observed under both the internal and external tibial rotation conditions.

For the pelvic rotation angle, no significant interaction between the ADIM condition and tibial rotation ( $F_{1,14}=$ 2.577, $p=$ 0.131) and no significant main effect of tibial rotation ( $F_{1,14}=$ 4.237, $p=$ 0.059) were found. However, the main effect of the ADIM condition was significant ( $F_{1,14}=$ 237.773, $p<$ 0.001). Under both the tibial internal ( $p<$ 0.001, $d=$ 3.45, CI $=$ 1.216–1.731) and external rotation ( $p<$ 0.001, $d=$ 3.01, CI $=$ 1.431–2.089) conditions, use of the ADIM significantly reduced the pelvic rotation angle during knee flexion.

4. Discussion

The present study demonstrated that ADIM led to greater EMG activity of MH and LH and lesser pelvic rotation while tibial internal and external rotations increased MH and LH muscle activities, respectively, during prone knee flexion. However, significant ADIM $\times$ tibial rotation interaction was found only in the MH muscle activity.

These study findings indicated that tibial internal and external rotation enhanced MH and LH muscle activities. Our results are consistent with those of Fiebert et al., who demonstrated that MH muscle activity increased during knee flexion with tibial internal rotation, and that LH muscle activity increased under knee flexion with tibial external rotation, when participants resisted a force equivalent to 5% of their body weight [15]. Lynn and Costigan reported that altering the tibial position during lower limb exercise could help selectively activate the MH or LH [3]. They explained that the hamstring muscle is responsible for producing rotations in the transverse plane of the knee, which influences selective activation of the MH and LH according to the direction of tibial rotation. Anatomically, tibial internal and external rotation respectively causes the MH and LH muscle fiber directions to be closer to line of action of each muscle. Muscle contraction is presumably reinforced when the muscle-fiber direction is closer to line of muscle action [16]. Overall, our data support previous findings that tibial rotation can be an effective strategy for improving the selective activation of the MH and LH.

With the ADIM, MH and LH muscle activities increased significantly increased during prone knee flexion with tibial internal and external rotation, respectively. An important compensatory action during prone knee flexion is anterior pelvic tilt due to excessive erector spinae muscle activity [6]. Unwanted anterior pelvic tilt can be prevented by the contraction of hamstring muscles because these muscles produce posterior pelvic tilt due to their common origin at the ischial tuberosity. Therefore, application of the ADIM in the present study might have facilitated hamstring muscle activation to maintain a neutral pelvic position against the pelvic anterior tilt force caused by knee flexion, thereby producing greater hamstring muscle activity during the ADIM compared to the non-ADIM condition. Another possible explanation for the present results may involve the influence of proximal stability on distal limb function [17]. Stabilization of the trunk, pelvis, and hip is necessary for specific limb movements during various functional activities [17]. Earl and Hoch demonstrated that proximally focused (e.g., trunk and hip) strengthening exercises increased hip strength and reduced the knee adduction moment in women with patellofemoral pain syndrome [18]. Those findings imply that proximal stability influences lower extremity movement patterns and improves lower extremity function. Therefore, we presume that application of the ADIM improved lumbo-pelvic stability and led to enhanced hamstring muscle function, thereby increasing hamstring muscle activity during prone knee flexion in the present study.

The present study demonstrated a significant ADIM $\times$ tibial rotation interaction during MH muscle activation. These findings indicated that the change in MH activation caused by application of the ADIM was greater during prone knee flexion with tibial internal rotation than during flexion with tibial external rotation. Considering the findings of previous studies and the present study, MH and LH muscle activities are greater under tibial internal and external rotation, respectively, during prone knee flexion [3, 4, 15]. Therefore, under the tibial external rotation condition, the contribution of the MH to the generation of knee flexion force might have been lower, regardless of ADIM application. Accordingly, an interaction between the ADIM and tibial rotation direction might have occurred during MH muscle activation. However, our results showed no significant ADIM $\times$ tibial rotation interaction during LH muscle activation. During prone knee flexion in the neutral tibial position, the LH contributes a greater proportion of the knee flexion force, compared with the MH [19]. Moreover, the range of tibial internal rotation is smaller than the range of tibial external rotation [20]. Based on the findings in previous studies, we hypothesize that LH muscle activity was involved in generating knee flexion force even under tibial internal rotation, due to the relatively small amount of tibial rotation compared with tibial external rotation. During application of the ADIM, therefore, greater LH muscle activation might have been enabled to maintain the neutral pelvic position under both tibial external and internal rotation, which might have resulted in minimal changes in LH muscle activation between tibial internal and external rotation conditions.

In the present study, pelvic rotation was significantly reduced when lumbo-pelvic stabilization was applied using the ADIM ( $p<$ 0.001). The ADIM is commonly used in lumbo-pelvic stabilization training programs [21, 22] and elicits preferential recruitment of the transversus abdominis muscle with minimal activation of the superficial trunk muscles [23]. Contracting the transversus abdominis muscle increases thoracolumbar fascia tension and intra-abdominal pressure, thereby enhancing lumbo-pelvic stability [24]. Therefore, we presumed that application of the ADIM would improve lumbo-pelvic stability via the preferential recruitment of the transversus abdominis, leading to reduced compensatory pelvic rotation movement. However, we found that the reduction in pelvic rotation angle (1.3–1.7 ${}^{\circ}$ ) during application of the ADIM was relatively smaller than that reported by Park et al. [6]. In the previous study, application of the ADIM reduced the pelvic rotation angle by 2.66 ${}^{\circ}$ during prone knee flexion in patients with low back pain. The difference between studies is likely due to differences in participant characteristics. In particular, the present study included healthy volunteers, whereas the previous study included patients with low back pain [6]. In patients with low back pain, greater lumbo-pelvic rotation and earlier lumbo-pelvic rotation were observed during prone knee flexion, compared with individuals who did not have low back pain [25]. Thus, patients with low back pain in the study by Park et al. presumably produced greater pelvic rotation, compared with the rotation in our healthy volunteers, during knee flexion without the ADIM. This difference might have resulted in relatively greater reduction in pelvic rotation during application of the ADIM during knee flexion [6].

There were several limitations in this study. First, participants were women. Notably, the range of tibial rotation differs between men and women [26]. Therefore, only women were included to avoid bias related to sex characteristics. However, to generalize our findings, further research recruiting more subjects, including males, will be needed. Second, this study did not investigate how tibial rotation ranges affected MH and LH muscle activities because participants performed maximum tibial internal and external rotation in this study. Considering that the previous study showed changes in hamstring muscle activity according to the degree of tibial rotation [27], measuring the tibial rotation angle may provide clinicians with detailed information on the hamstring activation pattern during prone knee flexion with the ADIM. Therefore, additional studies are needed to compare MH and LH muscle activities according to the degree of tibial rotation. Finally, although the ADIM was applied to improve lumbo-pelvic stability in this study, changes in trunk muscle activity that contributed to lumbo-pelvic stabilization were not measured during the ADIM.

5. Conclusions

Our findings showed that application of the ADIM led to greater EMG activity of the MH and LH, and reduced pelvic rotation, while internal and external tibial rotation increased MH and LH muscle activities, respectively, during prone knee flexion. These findings imply that a lumbo-pelvic stabilization strategy using the ADIM can reduce compensatory pelvic rotation and enhance selective activation of the MH and LH according to the direction of tibial rotation during prone knee flexion.

Footnotes

Conflict of interest

None declared.

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Effects of the abdominal drawing-in maneuver on hamstring rotational activity and pelvic stability in females

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Participants

2.3 Smartphone-based measurement tool (SBMT)

2.4 Procedure

2.4.1 Prone knee flexion without the ADIM

Table 1 Muscle activities of the medial and lateral hamstring muscles and pelvic rotation angles during prone knee flexion

2.5 Statistical analyses

3. Results

4. Discussion

5. Conclusions

Footnotes

Conflict of interest

References

Table 1
Muscle activities of the medial and lateral hamstring muscles and pelvic rotation angles during prone knee flexion