Leg strength improvement in elderly fallers and non fallers after eigth week of isokinetic strengthening

Transcription

1 BIOLOGY OF EXERCISE VOLUME 8.1, 2012 Leg strength improvement in elderly fallers and non fallers after eigth week of isokinetic strengthening D.O.I: SEMALTIANOU ELENI 1, KABITSIS CHRIS 1, HARAHOUSOU YVONNE 2, LAZOU VARVARA 3 1 Department of Physical Education and Sport Science, Serres, Aristotle University of Thessaloniki, Greece 2 Department of Physical Education and Sport Science, Komotini, University of Thrace, Greece 3 Institute of Chronic Diseases Rehabilitation Centre of Western Athens, Greece ABSTRACT The purpose of the present study was to investigate the effects of an eight week strengthening program in an isokinetic dynamometer, in the knee joint muscles of healthy elderly people, with and with out a history of falls. In the study participated 59 elderly men and women all in good health aged 60 years and over. The elderly were assessed in five concentric, two eccentric speeds (60, 90, 120, 180, 240 and 60, 120 /sec respectively) and in four angular positions (75, 60, 45, 30 of knee flexion, 0 = full extension) in an Cybex Norm isokinetic dynamometer. The experimental group of the study followed a strengthening program for quadriceps and hamstring muscles in the isokinetic dynamometer for eight weeks, in five concentric speeds. The results of the study indicated statistically significant differences (p.05) in strength and power between initial and final assessment in the experimental group. The results indicated also statistically significant differences (p.05) in strength and power between fallers and non - fallers of the experimental group in the initial assessment. These differences were diminished after the intervention period with fallers achieving statistically significant improvement (p.05). The results of the study provide evidence that an eight week isokinetic strengthening program of lower extremities in elderly people is very efficient in fall prevention. KEY WORDS: Fall Prevention, Elderly, Isokinetic Assessment, Lower Extremities.

2 58 JBE VOL. 8.1, 2012 INTRODUCTION Falls in the elderly are related to the effect of ageing process in the human body and particularly with muscle weakness, gait deficit, balance deficit, visual impairment, mobility impairment and reduced reflexes (25, 39, 49, 59). The frequency of falls increases with age and frailty level (49). About one third of the population above 65 years of age will experience at least one fall per year (25, 39, 49, 54). The probability of falls increases to 50% for elderly above 80 years. Elderly people who have fallen once, have two to three times higher probability of a recurrent fall. (38). Strength in the elderly Muscle strength is well known to be related to falls risk (49). Decline in muscle strength in the elderly, especially in lower extremities, is associated with increased risk for falls (24, 50). Muscle strength reaches its peak at the age of 20 to 30 years, and decreases gradually after the age of 40 (18). Strength decline rate increases gradually with each decade and is particularly pronounced after the age of 60 (16, 18). Strength continues to decline and after the age of 60 for both genders (16, 25). Healthy elderly people in the age of 70 to 80 demonstrate 20% to 40% less strength compared to young adults (25, 39) and also demonstrate an approximately 40% decrease in muscle fibers from 20 to 80 years (20). Muscle strength decreases at a greater rate for lower extremity than for the upper extremity (24, 41). Reduced maximum strength in the elderly (as a result of the ageing process), can be largely attributed to a reduction of muscle mass (sarcopenia) which is closely correlated with molecular, cellular, nutritional and hormonal changes in the human body (20, 34). The decrease of the muscle mass occurs due to the reduction of the number and also of the size of muscle fibers, particularly fast twitch muscle fibers (20, 21, 34). Reduced maximum strength in the elderly can also be attributed to the reduction of the quantity and the intensity of physical activity (28). According to the literature, strength begins to decline at different ages, in the different types of muscle contraction: muscle strength in concentric and isometric contraction begins to decline at around the fourth decade of life while eccentric begins to decrease gradually after the fifth decade of life and beyond (9, 22). The muscle strength decline rate is around 8-10% per decade for all muscle contraction modalities for both genders (16, 22). Muscle strength reduction follows different pace for each of the muscles of the human body. The decrease of strength, e.g. of the quadriceps and hamstring muscles is greater than the decrease of strength of the ankle muscles (53).

3 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 59 Lower extremities strength and falls in the elderly Falls is one of the most contributing factors of morbidity and mortality in the elderly. Muscle weakness is an important risk factor for falls in elderly population and a key factor for poor physical fitness and physical functioning (22, 43, 53). According to many researchers, decreased muscle strength of lower extremities, is an important risk factor for falls in community dwelling elderly (3, 21, 24, 39, 48, 49). Strength reduction is producing serious mobility problems in elderly people. Reduced strength of quadriceps and hamstring muscles (muscles of the knee joint), is often leading elderly to: inability to support the weight of their body in daily activities (23, 26), inability to restore the center of gravity inside the base of support in balance disturbance (58), inability to restore equilibrium after perturbation (18, 40, 56). These indications suggest an increased risk of falls in elderly (26, 43, 53). Reduced strength of the ankle joint muscles is often leading elderly to: inability to control the upright position (52), inability to control the sway of the body and restrain the centre of gravity inside the base of support, through the control of the generated torque around the ankle joint (52), inability to support body weight in everyday activities (23, 26, 52), inability to restore equilibrium after perturbation (40, 56, 59) inability of adequate thrust during gait (43, 53). According to the researchers, the differentiation of muscle strength of lower extremities among elderly who fall and those who do not fall also suggests that the reduced muscle strength of lower limbs is an important risk factor for falls (23, 26, 43, 52, 53). Reduced isometric strength of the quadriceps muscle (26, 43) and reduced isometric plantar flexion strength of the ankle muscles (43, 45) increase the risk for falls. Reduced isometric strength of the quadriceps muscle increases the risk of fractures in elderly people (30). Lower extremity strength improvement and fall prevention in the elderly Many studies indicated the positive effect of strengthening exercises of the lower extremities, in order to prevent falls in older people. Recent studies suggest that healthy elderly people who live independently in the community and have being involved in organized exercise programs, may improve muscle strength (4, 13, 24), walking (13, 26), balance (24) and possibly reduce the risk of falls (2, 50, 57). Many of the researchers, involved with lower extremity strengthening programs for elderly people in order to prevent falls, focused particular on the type, duration, frequency and intensity of exercise. Frequent observation of the researchers was that exercise programs should be adjusted to the specific demands of each individual. Due to this reason, a huge variety of methods and programs for strengthening of the lower extremities, is referred to the prevention of falls in the elderly (13, 15, 24, 33, 35, 43, 46, 57).

4 60 JBE VOL. 8.1, 2012 However, the effectiveness of many programs is yet unclear and many confusing elements are still present in the literature. Isokinetic assessment/strength improvement of lower extremities strength in elderly Very few studies until today have assessed lower extremities strength in elderly people with isokinetic dynamometry. The validity, reproducibility and accuracy of the measurements make isokinetic dynamometry unique for the evaluation of muscle strength. Additionally it is a very safe method for strength assessment in frail populations (i.e. elderly fallers) (6, 7, 31). Speeds that have been used for isokinetic assessment of the knee joint in elderly population are: 30, 60, 90, 180 /sec (9, 43, 45, 60), while speeds that have been used in the ankle joint are: 30, 60, 120, 180 /sec (5, 35, 43). Even fewer studies have adopted training in an isokinetic dynamometer as a strengthening method, for exercising frail elderly people in order to prevent falls, despite its advantages (5, 45). Because of the lack of evidence in this particular area of the literature, i.e. isokinetic exercise in elderly people and the confusing elements from the huge variety of strength intervention programs in the elderly, the present study constructed and applied an innovative isokinetic training protocol of eight week duration, for fall prevention in healthy elderly people. The aim of the present study was to investigate the effects of an eight week strengthening program through the use of an isokinetic dynamometer, in the lower extremities of healthy elderly people, fallers and non fallers, with the scope to prevent falls. MATERIALS AND METHODS In the present study participated 59 (N = 59) elderly men and women aged 60 years and over with or without a history of falls who were living in the community, with no major health problems. A sample of convenience was selected from the two major cities of Greece (Athens and Thessaloniki) in a collaboration project between the Aristotle University of Thessaloniki, the Institute of Chronic Diseases Rehabilitation Centre of Western Athens and the Elderly Open Care Centre of the surrounding Municipalities. All participants had to meet the following criteria to participate in the study: be free of serious musculoskeletal, neurological, cognitive, or other systemic disorders, as assessed by their physician, be able to walk with or without aids but without the assistance of another person and be able to follow simple instructions.

5 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 61 The experimental group comprised of 31 elderly, 6 men (n = 6) and 25 women (n = 25) and the control group comprised of 28 elderly, 5 men (n = 5) and 23 women (n = 23). From the total 59 participants (N = 59), 28 were included in the fallers group (n = 28) and 31 in the non fallers group (n = 31). As fallers were defined the elderly who have fallen one or more times the year prior to the study according to fall definition of Buchner et al. (1997). All participants had not participated in any organized exercise program the year prior to the study and all were informed about the purpose of the study and signed an informed consent. A Cybex Norm isokinetic dynamometer was used for strength and power assessment of the knee joint muscles of the elderly, for both legs. A full medical history report and a falls screening form which describes the frequency, nature and the injury (25), was completed by all the participants before the commencement of the study. The isokinetic assessment of the lower extremities followed the medical evaluation. The strength evaluator was blinded to the results of the screening form and medical questionnaire. The participants were examined in five concentric and two eccentric angular speeds (60, 90, 120, 180, 240 and 60, 120 / sec respectively) isokinetically in flexion and extension of the knee and in four different angular positions (75, 60, 45, 30 of knee flexion, 0 = full extension) isometrically, in flexion and extension. The lack of evidence in the literature, lead the researchers of the present study to the inclusion of all commonly used angular speeds and of all examined angular positions in the isokinetic and isometric assessment respectively. It also lead to the inclusion of all muscle contraction types (concentric, eccentric and isometric), in the strength and power assessment of the lower extremities of the participants (33, 43). The testing procedure was described in detail in previous article of the researchers (36). Peak torque and total work were recorded for both legs in concentric and eccentric contractions. Peak torque was recorded for the isometric contractions. The elderly of the experimental group followed an eight week strengthening program in an Cybex Norm isokinetic dynamometer. The exercise frequency was two isokinetic sessions per week and the elderly were trained in all concentric speeds (60, 90, 120, 180, 240 ) in both legs. Training sessions were supervised at all times. The exercise protocol, training frequency and duration of the training period were carefully designed. Their efficacy was carefully examined with a pilot study with nine elderly men and women a year prior to the present study. The results of the pilot study confirmed the effectiveness of the isokinetic strengthening program. Experimental and control group were assessed after the completion of the training period with the same isokinetic assessment protocol used in the initial testing.

6 62 JBE VOL. 8.1, 2012 Independent and paired samples t - tests were performed for the analysis of the data using the SPSS 17.0 statistical package. A 95% confidence interval was adopted for all statistical analyses. RESULTS Fifty nine elderly people participated in the present study (mean age: ± 2.49 years, mean height: ± 8.39 cm, mean weight: 69.37± 9.01 kg). Muscle strength and power differences between the two lower extremities An independent samples t - test was employed to examine the muscular performance of the two lower extremities of the elderly who participated in the study, in all angular speeds and in all angular positions of the assessment. The analysis was conducted in order to explore the existence of statistically significant differences between the two extremities in the non fallers and the fallers group which could indicate likelihood for falls. No statistical differences (p.05) were found in all variables entered in the analysis, except one (isometric peak torque ratio of flexors/extensors in 75 : t = 2.417, p =.018). From the isokinetic and isometric assessment occurred 72 variables for statistical analyses. In order to minimize the volume of the data for analysis and since there were no statistically significant differences (p.05) in the muscular performance of the two extremities in the isokinetic and isometric assessment, the mean score of the two extremities was adopted for all statistical analyses in all angular speeds and positions that were tested. Muscle strength and power differences between initial and final assessment A paired samples t - test was employed to examine the differences in isokinetic and isometric measurements after the intervention period, in the experimental group (n = 31). The analysis revealed statistically significant differences (p.05) in 34 of the 36 variables of the isokinetic and isometric assessment, with higher final assessment scores (Table 1). The same test in the control group did not reveal any statistically significant difference (p.05) in any variable. Muscle strength and power differences in the initial assessment between fallers/ non fallers in the experimental group The t - test for independent groups was then used to examine the differences between non fallers and fallers in all isokinetic and isometric mea-

7 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 63 surements in the experimental group in the initial assessment. The analysis returned statistically significant differences (p.05) in 32 out of the 36 variables, with the non - fallers group having higher scores in all isokinetic speeds and in all angles of isometric contractions, in flexion and in extension (Table 2). Muscle strength and power differences in the initial assessment between fallers/non fallers in the control group Once again the t - test for independent groups was used to examine the differences between non fallers and fallers in all isokinetic and isometric measurements in the control group in the initial assessment. The analysis did not reveal any statistically significant difference in any variable. Muscle strength and power differences in the final assessment between fallers/ non fallers in the experimental group The t - test for independent groups was then used to examine the differences between non fallers and fallers in all isokinetic and isometric measurements in the experimental group in the final assessment. The analysis returned no statistically significant differences (p.05) in all variables (Table 3). Muscle strength and power differences between initial and final assessment in non fallers of the experimental group The paired samples t - test employed to examine the differences in isokinetic and isometric measurements after the intervention period in the non fallers of the experimental group (n = 31) revealed statistically significant differences (p.05) in only 5 out of the 36 variables (Table 4). Muscle strength and power differences between initial and final assessment in fallers of the experimental group Once again the paired samples t - test was used to examine the differences in isokinetic and isometric variables after the intervention period, in the fallers of the experimental group (n = 31). The analysis revealed statistically significant differences (p.05) in all but one (35 of the 36) variables of the isokinetic and isometric assessment, with the scores of the final assessment being higher (Table 5).

8 64 JBE VOL. 8.1, 2012 Table 1: Paired samples t - test between initial and final isokinetic and isometric assessment in the experimental group.

9 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 65 Table 2: Independent samples t - test between fallers/non fallers in the experimental group in the initial isokinetic and isometric assessment.

10 66 JBE VOL. 8.1, 2012 Table 3: Independent samples t - test between fallers/non fallers in the experimental group in the final isokinetic and isometric assessment.

11 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 67 Table 4: Paired samples t - test between initial and final isokinetic and isometric assessment in non fallers of the experimental group.

12 68 JBE VOL. 8.1, 2012 Table 5: Paired samples t - test between initial and final isokinetic and isometric assessment in fallers of the experimental group.

13 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 69 DISCUSSION The main purpose of the present study was to investigate the effects of an eight week strengthening program in an isokinetic dynamometer, in the lower extremities of healthy elderly people with and without a history of falls. Isokinetic assessment is widely used. The validity, reproducibility and accuracy of the measurements make isokinetic dynamometry the most appropriate method for the evaluation of muscle strength. Additionally, it is a very safe method for strength assessment in frail populations (i.e. elderly fallers) (6, 7, 31). Concentric, isometric and eccentric movements were selected in order to best describe the length - tension and the force - velocity relationship of the lower extremities muscles. The selected speeds are the most commonly used speeds for evaluation of lower extremities in elderly people (7, 31, 33, 43). The innovation of the present study was the wide range of angular speeds (60, 90, 120, 180, 240 /sec in concentric and 60, 120 /sec in eccentric contractions) and angular positions (75, 60, 45, 30 in isometric contractions) used for the evaluation of the knee joint in the assessment protocol. Due to this wide range, the elderly were examined thoroughly in all possible speeds and possible positions they use in their every day life. Another innovation was the use of all muscle contraction modalities (concentric, eccentric and isometric contractions) in the lower extremity assessment of the elderly. Very few studies, to researcher s knowledge, have used more than two or three angular speeds and different muscle contraction types in order to assess elderly people. The most innovative and unique element of the present study was the isokinetic strengthening program for fall prevention applied to the elderly fallers and non fallers participants. The extensive review of the related literature did not reveal studies having used similar lower extremity strengthening programs in an isokinetic dynamometer in elderly fallers with the scope to prevent falls. Muscle strength and power differences between the two lower extremities According to researchers strength and power differences between the two legs are important intrinsic factors for falls in elderly people (39, 44, 45, 49). Muscle strength and power differences between the two legs are affecting step length and step velocity and consequently the walking cycle characteristics, thus increasing the risk for falls (61). Minimizing these differences contributes in correcting foot displacements or movement errors and plays an important role in fall prevention (39, 48, 49). The results of the present study revealed no statistically significant differences in strength and power between the two lower extremities. These results provide evidence that strength and power imbalances between the two legs are not responsible for the falls of the elderly of the current study.

14 70 JBE VOL. 8.1, 2012 For the statistical analysis 72 variables were used. In order to minimize the volume of the data for statistical analysis and since there were no statistically significant differences in the muscular performance of the two extremities in the isokinetic and isometric assessment, the mean score of two extremities was adopted for all statistical analyses in all angular speeds and positions that were tested. Muscle strength and power differences between initial - final assessment variables in the experimental and the control group The paired samples t - test used to explore the differences between initial and final assessment scores in the experimental group revealed statistically significant differences in all 36 variables, with the final assessment scores been higher. The same analysis did not reveal any differences between initial and final assessment scores in the control group. This finding suggests that the improvements in strength and power were due to the program applied. It is well documented that elderly, despite their frailty level, can improve their strength and power and their muscle cross - section area (i.e. muscle mass increase), after enabling in organized strengthening programs (4, 13, 15, 35, 37, 42). Strength and power gains depend greatly on duration, frequency, and intensity of the exercise program. According to the literature strengthening programs for lower extremities in elderly people aiming in strength and power increase, vary from several week to several months or even years of regular exercise (12, 21). Knee joint muscles strengthening programs from 8 to 12 weeks up to 10 to 15 months or even longer were applied in elderly people with positive results in strength gains (12, 13, 15, 35, 37, 42). Frequency of exercise plays also an important role. Researchers usually recommend exercise programs with three times per week frequency for satisfactory strength and power gain in lower extremities (12, 13, 15, 35, 37, 42). More recent studies have proved that exercise programs with two or even one time per week frequency can increase strength of the lower extremities, depending of the intensity of the exercise (46). Intensity of exercise is typically characterized as a percentage of a single maximal voluntary contraction (MVC) also known as a single repetition maximum (1RM) (15). Exercising programs for older people in high intensities have resulted in high increase of strength (2), with the most extreme increase reaching 227% (12, 15). Training in low intensities has resulted also in strength gains, but smaller ones, reaching approximately 20% strength increase (14). According to Hislop & Perrin, (1967) and to Thistle et al., (1967) isokinetic dynamometers allow individuals to exert as much force and angular movements as they can generate either large or small up to predeter-

15 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 71 mined velocity. This gives the advantage, muscle groups to be exercised in their maximum potential throughout a joint s entire range of motion working with very high intensity (19, 53). The strengthening program of the current study complied with the above prerequisites concerning proper duration, quantity and intensity of exercise, to be a successful and effective strengthening program. The leg strength and power improvement of the elderly who participated in the experimental group, combined with the fact that the elderly of the control group achieved no improvement, indicated the effectiveness of the program. According to the literature strength and power improvement of the lower extremity can prevent elderly from falls (2, 50, 57). Our study results indicated that the particular isokinetic strengthening program of eight week duration, two times/week frequency, with high intensity in five different concentric speeds (60, 90, 120, 180, 240 /sec) was efficient in increasing lower extremities strength and power in the elderly people of the study and therefore prevent them from falling. Very few studies so far are referred to isokinetic exercise in elderly and even fewer to isokinetic strengthening of the lower extremities in order to prevent falls. On the contrary, a vast number of studies are referred to strengthening programs of the lower extremities in elderly people with resistance devices. Assuming that fall prevention resistance exercises are similar to fall prevention isokinetic exercises our results can be compared to other studies results. In agreement with the above mentioned finding of the present study are the results of Rubenstein et al. (2000). They recorded the isokinetic torque of quadriceps and hamstring muscles of 59 elderly men aged 74 years and above, with or without a history of falls, with a Cybex 330 isokinetic dynamometer. They applied a lower extremities strengthening program with weight, twelve week duration. The results indicated that quadriceps and hamstrings muscles strength increased after the intervention period, thus decreasing the fall rate of the elderly from 13 to 6 falls per 1000 hours of activities for the elderly of the experimental group while the control group increased from 14 to 16.2 falls per 1000 hours of activities (35). Similar are the results of the study of Buchner et al. (1997) in a study with 105 women fallers, aged years. They recorded strength and power of the knee joint muscles with a Cybex II isokinetic dynamometer. They applied a six month strengthening program for the lower extremities of the elderly with weights, cycling and combination of weights and cycling. The results indicated that the experimental group increased strength and power of the knee joint muscles and decreased fall rate. The researchers concluded that exercise of lower extremities decreases falls in the elderly (2). In another study, Wu et al. (2002) examined among others, strength and power of the knee joint muscles, in 39 elderly over 65 years of age, 19 with a history of previous falls and 20 without. Twenty of the participants were fol-

16 72 JBE VOL. 8.1, 2012 lowing Tai - Chi lessons, of one hour duration, for the past three years. The researchers assessed in an isokinetic dynamometer strength and power of quadriceps and hamstring muscles in 60 and 120 / sec. The results of the study indicated statistically significant differences between elderly training in Tai - Chi and those who didn t in all angular speeds. The conclusion of the study was that long year exercising in Tai - Chi helps elderly maintains strength and power of the muscles, which are responsible for the upright position of the body, in a sufficient level (60). Muscle strength and power differences in experimental group between fallers/ non fallers in initial assessment variables In order to explore if strength and power differences in lower extremities are risk factors for falls in elderly population, an independent samples t - test employed for muscle strength and power differences between fallers and non fallers of the experimental group. The analysis revealed statistically significant differences in 32 of the 36 variables entered in the analysis with the non-fallers performing better than the fallers group. This finding provided evidence that reduced lower extremity strength and power are possibly important risk factors for falls in the elderly. Adequate strength and power of lower extremities are necessary elements for most of the every day activities of the elderly people. Reduced quadriceps and hamstring muscles strength can lead to insufficient support of the body weight in every day functional tasks, inability of balance recovery within the base of support in balance perturbations and makes elderly more susceptible for falls in static or dynamic balance changes (23, 26, 58). All the above indicate increased risk for falls in elderly people (21, 23, 26, 39, 43, 49, 52, 53). In agreement with the findings of the present study are the results of Perry et al. (2007). They recorded in a KIN - COM isokinetic dynamometer the concentric eccentric and isometric strength and power of the knee joint muscles in 44 healthy elderly without and 34 with a history of falls. The results indicated statistically significant differences with the non fallers performing better. The researchers concluded that reduced strength and power of lower extremities in the elderly increases the risk for falls (32). Similar with the results of the present study are the results of Trudelle- Jackson et al. (2006). In a study with 240 women, aged years with or without a history of falls they recorded falls, strength and power of the knee joint muscles. The results of the study indicated statistically significant differences in strength and power of hip and knee joint muscles. According to their results the researchers concluded that reduced strength of hip and knee muscles may increase the possibility for falls in the elderly (51).

17 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 73 In the study of de Rekeneire et al. (2003), the researchers assessed the quadriceps muscle of 3075 healthy elderly men and women fallers and nonfallers aged years. They examined the concentric torque of the elderly in 60 /sec in a KIN - COM isokinetic dynamometer. The results indicated statistically significant differences between fallers and non fallers, with non fallers performing better. The researchers based on their results concluded that: a) fallers exhibit less strength than non - fallers and b) depending from their lower extremity strength level, future fallers could be detected (8). Similar with the results of our study are the results of other researchers, reporting that non - fallers have better lower extremity strength and power values compared to fallers (2, 33, 39, 43, 48, 49). Muscle strength and power differences in experimental group between fallers/ non fallers in final assessment In order to explore if there were any differences between fallers and non fallers after the eight week training period an independent samples t - test employed. No statistically significant differences found in the final assessment of strength and power of the lower extremities after the intervention period. The initial low scores of the fallers of the experimental group were increased, reaching almost the same strength and power levels of the non fallers, thus diminishing the initial differences. The results of the study indicate the effectiveness of the intervention program in order to prevent falls. In agreement with the findings of the present study are the results of Chandler et al. (1998). In their study they assessed with a Cybex 6000 isokinetic dynamometer strength and power of the knee joint muscles in 100 elderly men and women with mean age 77.6 ± 7.6 years. The elderly of the experimental group followed a lower extremity strengthening program with elastic bands and body weight exercises, for ten weeks, three times / week, while the participants of the control group continued their normal activities. The results of the study indicated statistically significant differences in strength and power of knee joint muscles after the training period for the experimental group. The strength gain was statistically significant greater than the control group. Strength increased 10% to 16% for the experimental group and demonstrated about 1% increase to 3% decline for the control group. Strength gain was associated with gain in falls efficacy. The researchers concluded that strength gains could be achieved with simple resources and gain in strength in lower extremities had a positive effect in the ability of the elderly to avoid falls (4). Similar with the results of the present study are the results of Symons et al. (2005). In their research they assessed 12 elderly men and women aged

18 74 JBE VOL. 8.1, ± 7 in an isokinetic dynamometer (Biodex 3). They recorded isometric, concentric and eccentric knee joint muscles strength and power and among others stair ascending and descending time. They applied a strengthening program for lower extremities 12 week duration and 3 times/ week frequency in the isokinetic dynamometer. The results of the study indicated that elderly had statistically significant differences after the training program in strength and power and smaller ascending and descending time. The researchers concluded that isokinetic exercise is effective in strength increase in the elderly and in fall prevention, thus stair ascending/ descending poor performance is closely related with increased risk for falls (45). Muscle Strength and Power Differences in Faller and innon Fallers of Experimental Group between initial - final assessment variables Elderly non fallers exhibit high levels of strength and power in lower extremities compared to fallers (21, 23, 26, 39, 43, 49, 52, 53, 58). High levels of strength and power in lower extremities is correlated with high functional ability and small risk for falls (2, 33, 39, 43, 48, 49). The non - fallers group of the current study exhibited high strength and power levels - compared to those of the healthy adults from the initial assessment and consequently small risk for falls. After the intervention program their strength and power increased but not statistically significant. Their functional ability remained high and their risk for falls remained low as expected. A simple explanation can be given from the fact that in strength training gains are most pronounced when the subject is in a low state of fitness (1). Older individuals may be less trainable than young people but effects of training are noticeable even in very old age (1, 17). For the opposite reason mentioned for the non fallers group, the fallers of the present study exhibited statistically significant differences between initial and final assessment. The low level of their strength and power in lower extremities as recorded in the initial testing increased significantly, reaching almost the same strength levels of the non fallers, after the eight week strengthening program. According to researchers muscle strength depends on muscle size and coordinated activation of muscles by the nervous system. The largest muscle strength gains are noticed after the first few weeks of training (with the rate of increase in strength with continued training, declining) and probably attributed to improved motor control by the central nervous system (29, 55). Muscle mass increases after regular training at intensities exceeding 60-70% of their force generating capacity (1, 27). Researchers attribute that in

19 LEG STRENGTH IMPROVEMENT IN ELDERLY FALLERS AND NON FALLERS 75 both muscle cross - sectional area (hypertrophy) and in increase in fiber number (hyperplasia). The force capacity of each muscle varies with its cross sectional area (10). Trained individuals exhibit muscle hypertrophy, increasing the amount of strength they can generate (55). Once more, due to lack of evidence in the literature for isokinetic strengthening programs in elderly people and assuming that fall prevention resistance exercises are similar to fall prevention isokinetic exercises, our results can be compared to other studies results. In agreement with the finding of the present study are the results of Campbell et al. (1999). In their study they applied a 2 months strengthening program for the lower extremities with resistive exercises, with 3 / week frequency, in 233 elderly women 80 years and older. The researchers assessed lower extremities strength and fall rate of the elderly women and they also monitored them for the next two years. The results of the study revealed that lower extremities strength of the exercise group increased after the training period and resulted in a longitudinal reduction of falls over a two - year period. Falls reduced to one third from the first year and remained unchanged for two years. The researchers concluded that strengthening exercises in lower extremities prevent elderly from falls and this may be possible for a prolonged period (3). In the study of Ferri et al. (2003), the researchers assessed the strength and power of knee extensors of 16 healthy elderly men aged years before, during and after a 16 - week strengthening program for lower extremities, with resistive exercises. The results indicated an increase by 30% approximately in strength and power and 7.5% increase of cross sectional area (CSA) of knee extensor muscles. The increase in both strength and power and in CSA increased the elderly ability in performing their daily activities involving displacement of the body and decreased the risk for falls (11). CONCLUSION Isokinetic strengthening of the lower extremities is very efficient for fall prevention in elderly people. An isokinetic strengthening program can increase strength and power levels of the lower extremities in elderly fallers and nonfallers. Elderly fallers exhibit decreased strength and power compared to nonfallers. Elderly fallers with a low level of strength and power in lower extremities, can significant increase strength of the knee joint muscles even after a relatively short period (eight weeks period with two times per week frequency) of isokinetic training. Knee joint strength levels of elderly fallers can reach almost at the same level of strength with elderly non - fallers after a period of isokinetic training, thus minimizing the risk for falls.

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