Comparison Between Isotonic 1 Repetition Maximum Measurement With Isometric Muscle Strength Testing In Healthy Females
Comparison Between Isotonic 1 Repetition Maximum Measurement With Isometric Muscle Strength Testing In Healthy Females
1 repetition maximum (RM) and Maximum Voluntary Contraction (MVC) with digital dynamometer
 are popular method of measuring muscle strength. The types of muscle contraction involved in
 both are different, 1RM involves isotonic muscle contraction (ITMC) and MVC with digital
 dynamometer involves isometric muscle contraction (IMMC). There are several risks involved in
 measurement of 1RM, such as delayed onset muscle soreness (DOMS) and unsafe for pathological
 joints etc, this can be reduced if IMMC is used in measuring strength. Though both cannot be
 equated as they are different type of contraction, therefore the purpose of this study was to
 compare between 1RM measurement and isometric MVC using a digital hand-held dynamometer in
 healthy females. Twenty nine young females (mean age = 20.77 ± 1.28) without any weight
 training experience (mean BMI = 20.43 ± 1.85) volunteered for the study. It was a crossover
 trial where 48 hours of rest period was given between each measurement technique. The result
 showed moderate correlations (r = 0.365-0.847) between 1RM and MVC. A simple linear
 regression analysis revealed a significant estimated regression equation for dominant and
 non-dominant hands. [Dominant, Y=0.391x + 1.472; Non-Dominant, Y=0.251x + 2.629; (Y: 1RM, x:
 Isometric)] with low standard error of estimation value of (Dominant, 0.74; Non-dominant,
 0.80). The result also showed no significant difference between these derived equations and
 Brzycki 1RM prediction equation. Therefore, it was concluded that both prediction equations
 can be used interchangeably to predict the strength of a person, and thus IMMC can be used to
 predict 1RM in healthy females.
A dynamic isotonic muscle contraction (ITMC) causes joint movement and excursion of a body
 segment as the muscle contracts and shortens or lengthens under tension. One repetition
 maximum (RM) is defined as the maximum weight a person can lift only once in a complete range
 of motion. It is a gold standard for measuring muscular strength therefore it is used for
 most of the strength training programmes. The 1RM test has been shown to be reliable in
 various populations. Further, setting an intensity of resistance training based on a
 percentage of the 1RM has been found to be effective for improving outcomes such as muscle
 strength, muscle power, and muscle hypertrophy. Many studies have shown increase in strength
 when RM testing is repeated over several days to weeks. Therefore, most testing protocols
 suggest that strength should be measured more than once; typically 2 or 3 testing sessions is
 recommended.

 A familiarisation process prior to 1RM strength testing is necessary to ensure a reliable
 test result, this minimizes learning effect or systemic bias. It has been shown that without
 a familiarisation process prior to strength testing, there is a significant increase in the
 expression of muscle strength. In many studies, investigators have suggested that older
 individuals need 8-9 sessions of 1RM testing in order to increase the consistency of the 1RM
 measurements. Therefore, multiple familiarization sessions are beneficial for RM
 measurements. This draws us to a thought that such sessions may not be practical for studies
 examining training outcome to record the strength changes for several different resistance
 exercises as well as numerous other functional parameters. This unnecessarily increases the
 time requirement and extends the duration of the study, both of which might increase the
 likelihood of participant dropout in studies and loss of interest in exercise for clients. In
 the measure of 1RM, especially in patients, using a heavy weight and large number of
 repetitions imposes a greater risk of injury.

 Having been said that, 1RM measurement requires a long period of testing to have a consistent
 value; it also requires familiarization technique which is also very intense and extensive
 procedure. To avoid the risk, related to the measurement of 1RM, many studies have been
 conducted to produce regression equations for predicting 1RM strength. There are other
 studies too that have been undertaken to determine the accuracy of such equations. Prediction
 of 1RM strength allows an exercise specialist to assess an individual's maximal lifting
 capacity without subjecting the novice lifter to the increased risk associated with a 1RM
 lift. The advantage of calculating 1RM using the formula is that, it provides the therapist
 with the most widely accepted measure of strength without the risks associated with the
 formal 1RM testing. However the 1RM load lifting also requires great concentration and
 considerable mental preparation for the subject which can be an extremely intense experience
 that leaves them unsure and scared. Although there is no real data concerning the risk of
 injury in this test, the potential risk may be significantly increased by using very heavy
 loads.

 Testing 1RM uses isotonic movement which may be associated with increased risk of injury as
 it may include high speed of movement, inability to spread workload evenly over the entire
 ROM, unsafe for pathological joints, delayed onset of muscle soreness, requirement of
 equipment which can be expensive, and increased risk of injury, if the movement is done
 incorrectly. Measuring of 1 RM using the traditional way and by using prediction equation,
 both involve risk, therefore it brings us to an idea of the use of isometric type of movement
 in predicting 1RM.

 Isometric contraction 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 visible joint
 motion. It is a very popular method of testing the isometric strength of a particular muscle.
 It is a very easy, fast and accurate method of testing strength of a muscle. Isometric
 measurement by Lafayette Manual Muscle Test System (model 01163) has been proven to be highly
 reliable with in inter-class coefficient of 0.85. This method eliminates most of the risk
 factors that is observed in measuring 1 RM using the traditional way and the prediction
 equation. Furthermore, it is cost effective, more convenient to be done, and it does not
 aggravate sensitive joint surfaces. Therefore it reduces most of the risk involved in
 measuring 1RM using the traditional way and by using prediction equation. However, it is
 worth mentioning that, isometric strength measurement cannot be replaced with the 1RM
 measurement which is a dynamic method.

 Blazevich et al in their study of reliability and validity of two isometric squat (IS) tests,
 reported that IS with an isometric rack showed significant and high correlation (r = 0.77)
 with 1RM squat. However, when Demura, S studied the relationship between 1RM and isometric
 measurement of squat(IS), their study showed that some component (wide stance and parallel
 depth) of the squat correlated well with 1 RM whereas others did not. Simple linear
 regression analysis in their study revealed a relationship of Y = 0.992X + 30.3 (Y: 1RM, X:
 IS). This suggested that the IS using a back dynamometer may become an effective index for
 predicting 1RM squat. However, since the standard error of an estimate provided by the
 regression equation was quite large, (11.19 kg) therefore, it could not estimate 1RM in
 non-athletes; this study concluded that estimating a 1RM by Isometric squat using a back
 dynamometer maybe difficult. Though some studies have been conducted to estimate 1RM from
 isometric strength measurement, there is a dearth in literature to prove the same. Therefore
 the investigators aim to find out if isometric strength can be compared with 1RM in female
 subjects without weight training experience. Hence the purpose of this study is to find if
 there can be comparisons between 1RM (Brzycki's prediction equation) measurement and
 isometric MVC using a digital hand-held dynamometer in healthy females.
Inclusion Criteria:

 -  Healthy females

 Exclusion Criteria:

 -  musculoskeletal and neurological disorder

 -  history of high blood pressure

 -  heart disease

 -  rheumatologic disease that affected the mobility

 -  unstable cardio respiratorydisorder

 -  cardiovascular disorder