Muscle Function among Healthy Adult Athletes before and After a Postural Balance Training Period
Annika Larsson1* MSc, RPT, Börje Rehn2 Associate Professor, RPT, Sven Blomqvist3 PhD, RPT
1Umeå University, Sweden
2Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå University, Sweden
3Faculty of Health and Occupational Studies, University of Gävle, Sweden
Background:Postural balance training is primarily used by athletes as rehabilitation after previous injuries or for prevention.
Objective: The aim of this study was to investigate whether postural balance training can improve muscle function in healthy adult athletes.
Method: Seventeen healthy adult (6 males and 11 females) athletes between the ages of 21 and 50 years performed three postural balance exercises once a day 3x30 seconds per exercise on each leg. This intervention was performed daily for six weeks. Their muscle function were assessed with squat jump, heel rise and grip strength (control). Evaluation was done before and after the training period.
Results:Jump height, number of repetitions in heel rise and duration in standing on one leg increased with statistical significance. There were no improvements in postural sway and grip strength.
Conclusion: The results suggest that a postural balance training period can provide a better local muscle function regarding explosive strength and endurance among adult athletes even if postural sway is not affected.
Keywords: Muscle strength; Equilibrium; Exercise; Physical examination
Postural Balance Training (PBT) can be used as a rehabilitation training method for athletes after injury. The theory behind PBT is that the athletes’ bodies will become more stable and thereby better able to withstand impacts from external forces, which would otherwise increase the risk of reinjuries. Although the advantages of PBT are generally accepted, and it is seen as a training method to prevent and rehabilitate injuries , some training regimes for athletes does not includePBT. Athletes and trainers might be more motivated if it could be shown that the effects of PBT also improve muscle function to the advantage of their own sports.
Balance ability develops from childhood to adulthood and then reduces with increased age [2,3]. Older individuals have reduced strength and balance due to the naturally degenerative process [2-4]. This is especially due to a delayed anticipatory postural adjustment compared to younger individuals. However, the ability to recruit muscles may be intact . y being physically active, mainly with sport/tasks that challenge the postural system, it can lead to a retained balance even in older age . Studies have shown that strength training for elderly people improves the balance ability  and decreases the risk of falling .
During ordinary physical training there is an increase in strength which has been described to occur in two stages, but with overlap. In the first stage a process of neural adaptation occurs which facilitates a more efficient recruitment of muscle fibers . The second stage involves muscle fiber growth by increasing their cross-sectional area . Hypertrophy occurs in all fibers, however the fast twitch fibers has an 50% higher growth-capacity than slow twitch fibers . Especially the neural component involved in gaining strength may be trained by PBT.
The impact of PBT on physical performance in healthy individuals has been investigated in few studies in a variety of groups
The aim of this study was to investigate if postural balance training can improve strength, endurance, balance and grip strength in healthy adult athletes.
This was an experimental study with measurements before and after a PBT intervention. The inclusion criteria were; healthy adults between the ages of 18-50, active in sports at least three times/week for an on-going period of at least two years in conjunction to the intervention. Individuals being actively treated due to injury/pain in the lower extremities or lower back or with a history of injury within the past year were excluded. Individuals were prohibited from initiating any new training routine during the study.
Participants were chosen by self-selection. Information about the study was spread via posters in three nearby martial arts gyms, two gyms, two floor ball teams (one male and one female), all in Uppsala city-in Sweden- as well as in the Uppsala University´s department for physiotherapy. Information was also spread via e-mail to all physiotherapists working in the primary healthcare in Uppsala and to a middle school just outside Uppsala where many employees are physically active. The
At the pre-intervention test session, the participants drew a number from a sealed envelope and were thereby coded. The same physiotherapist (AL) performed tests before and after the intervention. The results from the test session were hidden until the post-intervention tests were complete.
Equipment and evaluation instruments
Muscle function was evaluated using a variety of functional tests. Squat jump (SJ)  was used to test explosive strength in the lower extremities and performed on a force platform. Heel rise [15,16] was used to measure endurance. Standing on one leg with eyes closed (SOLEC) [17,18] was used to assess both postural balance and endurance and was performed on a force platform. Grip strength was used to measure if therewas a more general increase in strength away from the lower extremities , caused by an increased central drive and usedas a control. Heel rise and SOLEC were tested on the dominant leg, which was chosen by the question “which foot do you kicka ball with”. Grip strength was tested with the dominant hand, the one that the participants used for writing.
Squat jump (SJ) is considered to have a good validity and reliability for adult, physically active men and was used in this study to assess vertical jump height [14,15]. SJ was performed on a force platform (Muscle Lab ET-FP-01) where jump height in centimetres was used as the outcome measure and measured by the time the participant was in the air, correlated
Heel rise has shown a good validity and reliability tested on young, healthy men [15,16].
In heel rise, participants stood on their dominant leg and were allowed to use the wall to maintain balance. The participants
Standing on leg eyes closed
SOLEC has a low validity but good inter-test reliability for healthy people .
SOLEC was performed on a force platform (see “squat jump”) and both maximum time standing on one leg and postural sway was measured. The participants stood on their dominant leg with the other knee flexed to 90 degrees in the knee and with their arms crossed over their chest. The test commenced when they closed their eyes and was stopped when the participant put the other foot to the ground or opened their eyes. After60 seconds, the test was aborted automatically . The time and the velocity of the centre of pressure (COP) in millimetres/ second were assessed. The participants performed three trials of which the longest length of time and least sway velocity was chosen for analysis.
Grip strength has been tested on healthy participants and has shown a high intra-test reliability . A grip meter (Sagitta)
The intervention included three postural balance exercises that were performed bilaterally once a day 3x30 seconds/exercise for six weeks. The first exercise was standing on one leg with the arms flexed forward to 90 degrees in the shoulder as the torso was rotated as far as possible to the left and right (Figure 1a). The second exercise was standing on one leg while the person had their eyes closed and the other leg and both arms in any chosen comfortable position (Figure 1b). In the third exercise, the participant stood on one leg with the other leg extended at the hip and the knee. The arms were kept above the head and the body was kept straight while the upper body tilted forward and the leg lifted up in the air-called “the dragon” (Figure 1c). Each participant was expected to keep a journal to gauge compliance. After three weeks, the difficulty of the exercises was increased by standing on a folded towel.
Figure 1a. Exercise 1. Rotation of the torso whilst standing on one leg.
Figure 1b. Exercise 2. Standing on one leg with both eyes closed
Figure 1c. Exercise 3. Standing on one leg, tilting the upper body down and raising the back leg.
To decide the number of participants required for this study design SJ was chosen as a main variable and a baseline was calculated on the first three participants included in this study. Five centimetres increased jump height was considered as a
Comparisons of outcomes pre- and post- intervention were made with a paired T-Test for normally distributed data and Wilcoxon´s test for the non-normally distributed data. Kolmogornov- Smirnov´s test was used to determine a normal distribution. The software was International Business Machine (IBM) SPSS version 20 for Windows. A p-value less than 0.05
Twenty-nine people expressed an interest in participating in the study, two of which did not meet the inclusions criteria. Three did not come to the testing appointment, one participant dropped out due to lack of time and one person were excluded from the study because the person could not decide her amount of exercise sessions/week. The final number of participating persons tested before the intervention was 22. During the intervention two subjects dropped out because they stated that the exercises were too hard and affected their normal physical performance adversely. Two other participants suffered from ankle distortion before the post-intervention test. Another participant forgot to do the exercises in the intervention and was excluded. At post-testing the final number of participants were 17. Their mean age was 32.4 (sd± 9.9).
Table 1. Mean values and standard deviations (sd) of pre-test and post-test for Squat jump, Heel rise, Postural sway, Grip strength and time in Standing on one leg eyes closed (SOLEC).
†Median value with corresponding dispersion measure. The Kolmogorov-Smirnov test confirmed a normal distribution of jump height, postural sway in SOLEC and maximal power in grip strength. Maximum time in SOLEC and number of heel rise repetitions were normally distributed before the intervention but not after.
The meanvalue centimetres in squat jump increased from 21.9 to 24 centimeters. The medianvalue in SOLEC and repetitions
The results of this study indicate that adult healthy athletes can improve their local muscle function with regards to strength and endurance by PBT exclusively.
Even though postural balance was trained the sway did not decrease significantly while the jump height and endurance did. It might be that an increase in strength will appear before sway decreases or that postural balance involves several physical aspects necessary for balance ability improves due to requirement of a more sophisticated neuromotor regulation for controlling sway. For regulation, coordination of the several muscles is required which might take a longer time to train and develop [20, 21]. It might also be that the training period was too short or postural sway is too difficult to improve for already active adult athletes. Behm et al  found that PBT improved postural balance after five weeks of training. Considering that the intervention in this study was conducted over a period ofsix weeks, it would have been expected also in this study. Another reason can be that these healthy adults need a certain amount of postural sway to regulate postural balance. More challenging balance tasks would give more information in this regard.
The exercises in this study were chosen specifically to work against the body weight alone and no additional weights were applied. Also, the exercises were performed with the knee in extension not allowing for dynamic muscle work around the thigh with strong postural muscles such as the quadriceps. Even if there were static exercises, strength gains for dynamic components improved. The improvements in strength are suggested to be due to local neuromuscular adaptation. Hypertrophy was not assumed and not measured. As there was unchanged grip strength, no improvements in the central drive could be an explanation for the gains in muscle function.
Lower extremity endurance increased as measured by the number of repetitions of heel rises and an increased time in SOLEC. According to the principle of specificity, this was expected and confirmed.
In previous studies, the effects of PBT were as a result of longer workouts, fewer times per week and for a period of four weeks [11-13]. Participants in this study had shorter training sessions, nine minutes per day, and therefore a longer intervention period was chosen. The time for each exercise was short (30 seconds) in order to decrease the risk of negative side effects such as muscle fatigue. Despite this, two participants who dropped out of the study stated fatigue as a reason.
It may seem like a low load shouldn´t affect the muscles in the lower extremities to that extent, especially since the participants in this study were physically trained. However, Bisson et al  has shown that static training generates more fatigue than isokinetic exercises, which is another reason for the choice to train only 30 seconds. Since training was performed on a daily basis it may have interfered with their normal training routine.
The total training volume in this study was 70 minutes/week. This in contrast to the load/duration in previous studies which often used fewer sessions/week [11-13] but up to an hour per session giving an effective total training volume of 120-180
A 5 centimeter´s difference on the SJ could be considered as a relatively high effect size. In the literature no real minimum difference for SJ is presented, which is why 5 centimeters was chosen based on clinical perspective and experience. This study did not reach up to the required number of participants and therefore, the insignificant results should be interpreted with caution. Another limitation was that the study did not have a control- or reference group. This means that results cannot be compared to a natural progression.
Several participants were not able to flex their knees to 90 degrees, often due to reduced mobility in the ankles. This could
The compliance was fairly high with an average of 35 sessions, to a maximum of 42. Despite this, the number of non-completed sessions may have affected the result negatively i.e. no effects on muscle function from PBT. This means that the improvements in this study could be underestimated.
The participants were not informed of their results to avoid an increase in effort just to have better results at the post-test. They could though have counted and remembered the number of heel rises in order to keep track of their progress. Therefore the test leader did not encourage them during any of the tests.
Even though postural sway was not improved in this experimental study, the result supports that it is possible to improve local muscle functions such as explosive strength and endurance in healthy, adult athletes by only utilizing regimes for postural balance training.
Cite this article: Annika Larsson. Muscle Function among Healthy Adult Athletes before and After a Postural Balance Training Period. J J Sport Med. 2016, 3(2): 021.