Falls are considered the most common geriatric syndrome (Chang et al., 2010; Legters et al., 2006) and they are often related to mobility, as well as to neurological and cardiovascular causes (Lord et al., 2003). The structural changes that occur as a result of aging imply an important decrease in physical condition (Katsura et al., 2010). These facts have a negative influence on functional balance, interfering with essential daily activities such as bathing, getting dressed, and climbing or descending stairs (Lacour, 2000). Anticipating the causes that limit functional balance can be relevant, given that around 30% of falls result in an injury that requires medical attention (Berry and Miller, 2008). Health care costs for treatment of fall-related injuries was 1.85 times higher than the cost of implementing a fall prevention program (Hektoen et al., 2009), and a few fall prevention studies reported a positive effect on the quality of life (Host et al., 2011; Vaapio et al., 2009).
Studies in older adults have shown a relation between the lack of muscle flexibility and poor walking ability and body balance (Iwamoto et al., 2009). It has been described that greater efficacy of the lumbopelvic muscles can contribute to postural stabilization (Cosio-Lima et al., 2003). Balance improvement is associated with decreased risk and fear of falling, and with an improvement in quality of life (Chang et al., 2010; Legters et al., 2006). In the last few years, several training programs based on aquatic exercises (Katsura et al., 2010), or on a peer-led model have helped subjects maintain strength and balance levels (Waters et al., 2011), thus contributing to reducing falls in older people. More precisely, proprioceptive exercises on unstable surfaces (Swiss ball or BOSU) have been shown to improve flexibility, balance and lower-limb strength in sedentary women (Sekendiz et al., 2010), as well as providing a basis for a muscle strength increase (Teixeira et al., 2010). Martinez-Amat et al. (2013) showed how a 12-week proprioception training program in older adults caused improvements in stabilometric measures such as Romberg surface and Romberg speed as recorded with unstable platforms. Westlake and Culham (2007) also reached the conclusion that, in older adults, there was a short-term enhanced postural response to proprioceptive reintegration following a sensory-specific balance exercise program. Such exercises are based on the potential increase of muscle activity produced by maintaining postural stability, as the decrease in the unstable surface contact area leads to increased muscle recruitment (Marshall and Murphy, 2006).
Although all types of training (traditional strength training, functional strength training, endurance training) can enhance physical capacity in older adults (Solberg et al., 2013), there are many studies that have found a more specific association between physical activity and balance ability (Cadore et al., 2013; Katsura et al., 2010) or risk of falling (Chang et al., 2010; Teixeira et al., 2010). Nevertheless, some other studies revealed no conclusive differences in training between stable and unstable surfaces (Uribe et al., 2010). It is important to note that most of the studies mentioned above establish a general relation between training and fall prevention. More specifically, Granacher et al. (2008) concluded that in the near future, strength training could be replaced by high-velocity forms of power training and balance training by perturbation-based training programs. Nevertheless, to our knowledge, there are no studies showing the degree of influence of proprioceptive-training-improved physical abilities (flexibility, balance, and strength) on balance ability and on the risk of falls in older adults.
In light of the research mentioned before, the purpose of the present controlled trial was to determine the effects of a 12-week proprioceptive training program on the improvement of flexibility, balance and lumbar strength (primary outcome) as well as to analyze the association between flexibility, balance and lumbar strength, and balance ability and risk of falls (secondary outcome) in older adults.
The present study was a controlled, longitudinal trial in which participants were allocated to the intervention (n = 28) or usual care (control) group (n = 26). For practical and ethical reasons, it was not possible to randomise the patients. We had an ethical obligation with the Andalusian Federation of Older People's Associations (Spain) to provide treatment to all older adults willing to participate in the study, but due to limitation of resources, we created a waiting list. Older adults from the waiting list agreed to be part of the usual care group (control group) and were offered the intervention program at the end of the intervention period. Data collected only during the control period were included in the current analysis. The research protocol was reviewed and approved by the Ethics Committee of the Master's degree in Research and Teaching in Physical Activity and Health Sciences (University of Jaen, Spain). The study was carried out from March 2010 to June 2011, following the ethical guidelines of the Declaration of Helsinki (2008 revision).
A total of 208 older adults who attended the Andalusian Federation of Older People's Associations were contacted. Sixty-eight potentially eligible older adults responded, and gave their written informed consent after receiving detailed information about the research aims and study procedures. Subjects who were 65 years or older and able to follow simple directions (e.g., left, right, up or down) were included in the study. The exclusion criteria were functional blindness (acuity level worse than 20/200) and major chronic medical or physical conditions, including rheumatoid arthritis or osteoarthritis, severe low back pain, severe lower-limb deformities, as diagnosed by a physician, which might result in the inability to ambulate independently or with the use of an assistive walking device.
A total of fourteen patients were not included in the study (eight had physical activity contraindications, two had locomotion problems, and two reported schedule problems). After the first day of baseline measurements, two patients refused to continue participating. Therefore, a final sample of 54 older adults started the study. The study flow of patients is presented in Figure 1. The baseline characteristics of participants in both the experimental and the control groups are shown in Table 1.
The subjects in the experimental group participated in a 12-week proprioception training program, performed two days per week (Monday and Wednesday), for a total of 24 sessions. Participants in the control group performed the same amount of usual physical activity as the experimental group (2 days/week). Subjects in the control group were also requested not to change their usual levels of activity and their medication for the 12-week intervention period. All participants (both control and experimental) met weekly for an hour with the researchers to discuss topics of interest to the elderly. The exercise sessions were carefully supervised by a fitness specialist and by a physical therapist who worked with groups of 10-12 people.
Each exercise session included 50 minutes (10 minutes of warm-up with slow walk, mobility and stretching exercises, followed by 30 minutes of a proprioceptive exercises program, and finishing with 10 minutes of cool down through stretching and relaxation exercises). The training program comprised six specific proprioceptive exercises, each five minutes long, which were conducted in static and dynamic positions for a period of 30 minutes (Figure 2). The training was structured into two or three progressive phases according to the type of exercise. The initial phase comprised weeks 1-5, the intermediate phase weeks 5-8, and the...