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Comparison of electrical stimulation and isometric training on isokinetic strength of knee extensors: A randomized clinical trial.

Byline: Emre Baskan, Ugur Cavlak and Hasan Huseyin Yildiz

ABSTRACT

Objective: The purposes of this study were (1) to investigate and (2) to compare effects of isometric exercises and electrical stimulation on isokinetic strength for healthy quadriceps femoris muscle.

Methodology: Twenty healthy volunteers (range, 20-25; mean age, 20.9+-1.1 yr) participated in the study. All participants were divided into two groups (Group I and Group II). Each group consisted of 10 subjects. While Group I received electrical stimulation with Russian current, Group II trained with maximal volunteer isometric exercises (10s contraction and 50 s relaxing periods with 10 repetitions) for three days per week for six weeks. Before and after the training program, each subject was evaluated using the following tests; anthropometrical measurements, fixed weight repetition, step-up, decline squat, single leg hop, and isokinetic assessments (peak torque, work per repetition, initial peak torque, fatigue index, total work done, %BW).

Results: After a 6-week training program, significant differences in terms of physical functioning and isokinetic parameters in the two groups were found (pLess than0.05). Physical functioning and isokinetic strength of quadriceps femoris muscle were seen to be increased in two group after training programs (pLess than0.05). There were no significant differences between the groups (pgreater than0.05). Quadriceps femoris hypertrophy was only found in electrical stimulation group (pLess than0.05).

Conclusion: The results obtained from this study show that the two strengthening techniques just used in the study can be used to improve muscle strength, performance and isokinetic parameters in healthy quadriceps femoris muscle (pLess than0.05). But, there is no superiority on each other. In conclusion, these results indicate that electrical stimulation and maximal volunteer isometric exercises can be used to increase isokinetic strength as an alternative for isokinetic dynamometer in clinical setting.

KEY WORDS: M. Quadriceps Femoris, Electrical Stimulation, Isometrical Exercises, Isokinetic Testing, Strength, Endurance.

How to cite this article: Baskan E, Cavlak U, Yildiz HH. Comparison of electrical stimulation and isometric training on isokinetic strength of knee extensors: A randomized clinical trial. Pak J Med Sci 2011;27(1):11-15

INTRODUCTION

Quadriceps femoris (QF) muscle frequently trained in physical therapy clinics. Muscle strength is a com-plex phenomenon to characterize because of its wide range of normal variability and the fact that strength is affected by many factors, such as sex, age, test position, and type of contraction. The ability to Ugur Cavlak et al.

Measure changes in muscle strength.1 Well con ditioned muscle and muscular balance are needed to attenuate impact loads and provide joint stability.2 QF muscle strength is important for human body stability, movements and sports activi-ties. Therefore, to protect and improve QF muscle strength is vital.

Following injuries to joints and muscles the injured parts of the body are often immobilized for some time to allow the damaged joints and muscles to heal. While immobilization is usually necessary, it has deleterious consequences on the function of muscles, and recovery is often slow because muscles have deteriorated during the period of immobilization. It is in these cases that electrical stimulation (ES) of muscles during the period of immobilization and afterwards is beneficial and speeds up recovery.3,4 Electrical stimulation devices have been advertised to increase muscle strength, to decrease body weight and body fat, and to improve muscle firmness and tone in healthy individuals. It produce more muscle contraction than voluntary contraction.5,6 Isometric exercise is a static form of exercise in which a muscle contracts and produces force without an appreciable change in the length of the muscle and without vis-ible joint motion.

Based on the early research it was reported that isometric strength gains of 5% per week occurred when healthy subjects performed a single, near-maximal isometric contraction everyday over a 6-week period.7

The purposes of this study were to investigate and to compare the effects of isometric training and elec-trical stimulation on functional and isokinetic strength of knee extensors in healthy subjects.

METHODOLOGY

Twenty healthy volunteers (mean+-SD age 20.9+-1.1 yrs) participated in the study. All participants were divided into two groups of 10 subjects. Group I re-ceived electrical stimulation of the quadriceps femo-ris muscle on the dominant side without voluntary effort associated with Russian current (2500Hz). The current was increased to provide tethanical contrac-tion (10 repetitions of 10s contraction with 50s rest periods in between) for three days per week for six weeks. Group II trained with maximal voluntary iso-metric knee extensions (10 repetitions of 10s with 50 s relaxing periods in between) for three days per week for six weeks. Subjects in both groups trained at 60deg knee flexion angle.

Before and after both training programs, each subject was evaluated using the following tests: (1) Anthropometrical tests; quadriceps circumference measurements (5cm and 15cm above the kneecap) were used to assess muscle hypertrophy on domi-nant side.8 (2) Fixed weight repetition test (seated with back support with hip and knee at 90o flexion position) was used. The subjects examined with con-stant 10p weight until fatigue came out and the num-ber of repetitions was recorded.9 (3) Step up test; sub-jects were asked to stair up and down 45cm height step on dominant leg. The number of repetitions was recorded.10 (4) Decline squat test; subjects performed single-leg eccentric squats at decline angles of 25deg on a board for decline squat test. All performed the de-cline squat standing on their dominant leg and flex-ing their knee, starting from complete extension to maximal flexion. The contralateral leg was kept for-ward during the downward movement.

Subjects came back to starting position by placing the con-tralateral leg. They were instructed to keep their trunk in an upright position and to avoid lateral weight shift.11 (5) Single leg hop test; subjects per-formed a single leg hop for distance with dominant leg. After demonstration, each subject was allowed one trial dominant leg. Beginning with the toes im-mediately behind the starting line, subjects per-formed one hop to complete a trial. The hop was measured from the starting line to the end of the toes after completion of a trial. Dominant leg was tested three times with the average distance scored for each subject.12 (6) Isokinetic tests; isokinetic muscle mea-surements were performed using the Biodex System dynamometer (Cybex II) with the knee attachment on. Orientation of the dynamometer was kept at 0deg, tilt at 0deg, and seat orientation at 0deg. Before the testing procedure, all the subjects performed conditioning exercises and stretching of the lower extremities to warm up.

They then exercised on a bicycle for 10 minutes. They were seated and secured to the appa-ratus with straps across the chest and thigh. Each time, the attachments of the dynamometer were re-adjusted accordingly, so that the centre of motion of the lever arm was aligned as accurately as possible with the slightly changing flexion-extension axis of the joint. The resistance pad was placed on the distal tibia.

The range of motion of the knee joint was set at 0-90deg. Dominant leg isokinetic (concentric/ concen-tric) knee flexion and extension studies within the protocol of 60deg/s (five repetitions), 180deg/s (15 rep-etitions) were accomplished. Between the two ses-sions, subjects rested for 20 seconds. Vocal encour-agement during the tests was consistent and stan-dardized. Flexion and extension peak torque and work per repetition values, total work done, %BW

Isokinetic Test Values###Before Training###After Training###Wilcoxon

###Mean +- SD###Mean +- SD###Z###P

Peak Torque(Nm)###117.1 +- 50.0###136.8+- 44.0###-2.805###0.005

WPR (Nm)###117.5 +- 55.7###141.8 +- 52.1###-2.803###0.005

Initial Pek Torque###43.5 +- 27.4###70.5 +- 28.6###-2.803###0.005

Fatique Index###-37.9 +- 60.5###23.6 +- 8.8###-2.701###0.007

Total Work Done###823.1 +- 441.9###1024.8 +- 484.6###-2.599###0.009

Peak Torque %BW###1299.9 +- 693.6###1668.9 +- 670.3###-2.803###0.005

and fatigue ratios automatically calculated by the device were noted.

All participants gave informed consent and the study was approved by the ethical board committee of Pamukkale University Medical Faculty (Ref no: 06.2; date, 03.06.2009). This study was supported by Pamukkale University Scientific Research Projects Foundation (Grant no: 2009SBE004).

Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS version 13.0). Mann-Whitney U Test was used for comparing the groups. Wilcoxon test was used to detect improvements within groups. The pLess than0.05 level was used to denote statistical significance.

RESULTS

After a 6 -week training program, significant differences in terms of physical functioning and isokinetic parameters in the two groups were found (pLess than0.05) . There were no significant differences between the groups (pgreater than0.05). Although quadriceps femoris hypertrophy was only found in electrical stimulation group, (pLess than0.05) this difference was not significant statistically when the groups were com-

pared. On anthropometrical measurements was found hypertrophy on 15cm above the kneecap on electrical stimulation (pLess than0.05), fixed weight repetition significantly increased (pLess than0.05), step up test significantly increased (pLess than0.05), decline squat (pLess than0.05), single leg hop (pLess than0.05) significantly in-creased on both groups. On isokinetic tests peak torque (pLess than0.05), work per repetitions (pLess than0.05), total work done (pLess than0.05), %BW (pLess than0.05) and fatigue in-dex (pLess than0.05) were increased on both groups. In other saying, physical functioning and isokinetic strength of quadriceps femoris muscle were seen to be in-creased in two group after training programs (pLess than0.05) (Table I and II).

DISCUSSION

There is general agreement in the literature that isometric strength training and electrical stimulation develops strength and are beneficial for both prevent-ing and treating many types of therapeutic injuries. However there are few studies which investigated effects of electrical stimulation and maximal volun-tary isometric contraction (MVIC) on isokinetic strength on literature.13 Most studies indicate that ES

###Table--II: MVIC Test Values.###

Isokinetic Test Values###Before Training###After Training###Wilcoxon

###Mean +- SD###Mran+- SD###Z###P

Peak Torque(Nm)###142.8 +- 51.9###157.5 +- 52.5###-2.805###0.005

WPR (Nm)###135.7 +- 46.6###162.0 +- 56.5###-2.705###0.007

Initial Pek Torque###47.4 +- 31.8###81.8 +- 36.97###-2.701###0.007

Fatique Index###-86.6 +- 179.5###22.0 +- 52.0###-2.091###0.037

Total Work Done###857.9 +- 416.3###1269.8 +- 520.1###-2.803###0.005

Peak Torque %BW###1314.8 +- 495.8###1898.6 +- 505.7###-2.803###0.005

Ugur Cavlak et al.

Is more effective in preventing muscle atrophy when compared to no exercise, isometric exercise of the quadriceps muscle group, isometric co-contractions of both hamstrings and quadriceps groups and combined isometric exercise.14 Examination of the literature reveals certain common characteristics among studies of electrical stimulation for augmen-tation of muscular strength. On the other hand many investigators have used electrical stimulation to produce tetanic muscular contractions.15

According to Delitto, patients in an electrical stimu-lation regimen can achieve higher individual thigh musculature strength gains than patients in a volun-tary exercise regimen when simultaneous contrac-tion of thigh muscles is prescribed during an early phase of postoperative rehabilitation.16 Mohr et al investigated comparison of isometric exercise and high volt galvanic stimulation on quadriceps femo-ris muscle strength. The Isometric Exercise Group was found to have an increase in strength signifi-cantly greater than either the Control or Electrical Stimulation Group. No increase in strength was ob-served in either the Control or Electrical Stimulation Group.

This study indicates that HVG stimulation is not as effective as isometric exercise in increasing strength in muscle.17 Ogino et al designed study for MRI quantification of muscle activity after volitional exercise and neuromuscular electrical stimulation. They found volitional muscle contractions were sev-eral times stronger than those induced by neuro muscular electrical stimulation (NMES) in this study and their findings support the idea that MRI can pro-vide a noninvasive way to quantitative and localize volitional and electrically stimulated muscle activa-tion.18 Baskan investigated effects of MVIC at differ-ent knee angels (15o, 60o) on healthy QF muscle. Af-ter six week training periods strength and endurance improved statistically significant on QF muscle on both groups. But 60o knee angles are more effective than 15o.19

In our study after ES and MVIC training improved the muscle strength and performance (pLess than0,05) but there were no differences between the groups (pgreater than0,05). Perez et al investigated the effects of electrical stimulation (ES) on oxygen uptake (VO2) kinetics and delta efficiency (DE) during gradual exercise. The hypothesis was that ES would attenu-ate the VO2-workload relation and improve DE. After the study they explained ES could be used as a supplementary tool to improve two of the main determinants of endurance capacity, namely VO2 kinetics and work efficiency.20 Some authors proposed to determine skeletal muscle structure and function in response to electrical stimulation in mod-erately impaired COPD patients. NMES may pro-mote a modest degree of type II muscle fibre hyper-trophy in COPD patients with well-preserved func-tional status.

These micro-structural changes, how-ever, were not translated into increased volitional strength in this sub-population.21 We found that af-ter the strength training program fatigue values de-creased on both groups (pLess than0,05). Hypertrophy ap-peared on ES group (pLess than0,05) but there was no dif-ferences on MVIC group (pgreater than0,05). The results ob-tained from this study show that the two strength-ening techniques used in the study can be used to improve muscle strength, performance and isokinetic parameters in healthy quadriceps femoris muscle (pLess than0.05). However, there is no superiority on each other. These results indicate that electrical stimula-tion and maximal volunteer isometric exercises can be used to increase isokinetic strength.

Currier et al investigated effects of electrical stimulation and isometrical exercises on healthy sub-jects for quadriceps femoris muscle. Five weeks later they found isokinetic strength improvement at all groups but there were no differences between the training groups.15 Another study investigated elec-trical stimulation's effectiveness even in improving quadriceps strength in healthy subjects and com-pared interferential and low-frequency current in terms of the effects on quadriceps strength and per-ceived discomfort. Group A received electrical stimu-lation with bipolar interferential current while group B received electrical stimulation with low-frequency current. Group C served as the control group. Statis-tically significant increase in isokinetic strength was observed after training in two groups.

Increase in strength did not differ between the stimulation groups. No significant change in strength occurred in group C. 22 We also found that ES and MVIC im-proved the QF muscle performance and strength (pLess than0,05) but the differences between the two groups were not significant (pgreater than0.05). Isokinetic parameters significantly increased on both groups (pLess than0.05). Moreover, QF hypertrophy associated with increased formation with isokinetic strength and endurance (pLess than0.05). The results obtained from this study indi-cate that electrical stimulation and maximal volun-tary isometric exercises can be used to improve the functional outcomes assessed by performance tests and dynamic isokinetic strength in healthy subjects. These results indicate that electrical stimulation and maximal volunteer isometric exercises can be used to increase isokinetic strength as an alternative for isokinetic dynamometer in clinical setting.

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Authors' Contributions: EB completed the study design, manuscript writing, and statistical analysis.

UC did study management, editing of the manu-script, review and final approval of manuscript. HHY did data collection and analysis of the data.

Grant Support & Financial Disclosures: This study was supported by Pamukkale University Scientific Research Projects Foundation (Grant no: 2009SBE004).

Authors:

1. Emre Baskan, PT, PhD.

2. Ugur Cavlak, PT, PhD, Professor.

3. Hasan Huseyin Yildiz, MD, Department of Physical Medicine and Rehabilitation, Servergazi State Hospital, Denizli, Turkey.

1-2: School of Physical Therapy and Rehabilitation, Pamukkale University, Denizli, Turkey.

Emre Baskan, Ugur Cavlak, Hasan Huseyin Yildiz Correspondence: Dr. Ugur Cavlak, Pamukkale University Fizik Tedavi ve Rehabilitasyon, Yuksekokulu Kinikli Kampusu Rektorluk Binasi B Kati, 20070 Denizli, TURKEY. E-mail: ucavlak@pau.edu.tr Received For Publication: July 3, 2010 Accepted: September 25, 2010
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Author:Baskan, Emre; Cavlak, Ugur; Yildiz, Hasan Huseyin
Publication:Pakistan Journal of Medical Sciences
Article Type:Clinical report
Geographic Code:9PAKI
Date:Mar 31, 2011
Words:3299
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