Abstract
Non-skid socks and external weight are commonly utilized in healthcare and training to improve stability and simulate real-world conditions. However, their combined effects on postural response during perturbation remain unclear. This study examined how non-skid socks and added anterior weight affect latency and amplitude responses during postural perturbations. Ten healthy participants (mean age 24.5 ± 4.38 years) underwent randomized perturbation conditions with and without non-skid socks and 10% body weight applied via weighted vests. Results from two-way ANOVA and mixed-effects models revealed no significant effects of socks, weight, or their interaction on latency (p > 0.05). However, amplitude analysis showed a significant interaction (p < 0.001), indicating that the combination of socks and weight increased postural instability. Specifically, conditions involving non-skid socks and weight resulted in higher amplitudes, suggesting greater deviations of the center of gravity and increased fall risk. Conversely, non-skid socks alone reduced amplitude, enhancing stability compared to barefoot conditions. These findings highlight the nuanced effects of non-skid socks and added weight on balance and stability. While socks alone may improve postural control, their combination with weight appears to elevate instability. Future research should include larger, diverse samples to confirm these findings and guide clinical practice regarding non-skid socks and weighted training protocols.
Keywords: Non-skid socks, postural stability, perturbation, weight training in healthcare
INTRODUCTION
Reaction time is a fundamental aspect of human performance, influencing activities ranging from everyday tasks to specialized movements in sports and rehabilitation settings. Understanding the factors that impact reaction time, such as environmental conditions and individual physical attributes, is essential for optimizing performance and ensuring safety. Among these factors, sudden disturbances or alterations in stability, known as perturbations, play a critical role in determining how effectively individuals can respond to balance challenges. This issue is particularly relevant in fall prevention, as falls represent a significant health concern, especially among older adults and individuals with compromised balance. Each year, approximately 319,000 elderly individuals are hospitalized due to fall-induced hip fractures[1].
A common and cost-effective intervention aimed at reducing falls is the use of non-skid socks, which are marketed as enhancing balance, stability, and confidence during ambulation. However, empirical evidence supporting their effectiveness remains limited. Research indicates that non-skid socks do not significantly improve balance or stability in healthy individuals and offer minimal protection against falls[2]. Despite these findings, non-skid socks continue to be widely used in hospitals as an anti-fall measure[3] and are prominently sold by major retailers such as Lululemon (shop.lululemon.com) and Adidas (adidas.com). In addition to footwear, external anterior weight placement has been explored as a factor influencing postural stability and fall risk. Shifting the center of gravity forward through added anterior weight can destabilize posture and increase the risk of falls, particularly in populations with impaired balance[4, 5]. Understanding how anterior weight affects balance is essential for evaluating fall prevention strategies and improving rehabilitation protocols. The interplay between non-skid socks and added anterior weight introduces a complex dynamic that may influence reaction time and balance control. Non-skid socks may alter friction and ground interaction, while external weight changes the biomechanical response by shifting the body’s center of mass and influence ground reaction force as well. Although prior research has examined these factors independently, few studies have investigated their combined effects on reaction time during sudden perturbations [2]. This gap highlights the need for a comprehensive evaluation of how these elements interact to influence postural stability.
In this study, we seek to explore the combined effects of non-skid socks and added anterior weight on reaction time and body responses to sudden perturbations during quiet stance. We aim to provide evidence-based insights into the practical utility of these interventions in healthcare and athletic settings. We hypothesize that participants wearing non-skid socks and carrying anterior weight will exhibit delayed reaction times due to increased biomechanical and sensory demands.
MATERIALS & METHODS
The study included 10 participants, consisting of 5 males and 5 females (Table 1). All participants were healthy, and had no fall-risk. Before participation, they provided written informed consent approved by the Chapman University Institutional Review Board (IRB).
Table 1.
Anthropometric table with mean and standard deviation of Age, Height, and Weight
| Parameter | Mean | Standard Deviation |
|---|---|---|
| Age (years) | 24.5 | 4.38 |
| Height (cm) | 170.43 | 6.04 |
| Weight (kg) | 73.46 | 12.01 |
The added anterior weight for each participant was calculated as 10% of their body weight. Metal ingots weighing 0.18 kg each were placed into the weighted vest, which itself weighed 0.64 kg (Table 2). Participants were provided with non-skid socks and were instructed on when to wear the socks and the weighted vest based on assigned randomized conditions. These conditions involved different combinations of wearing socks and the weighted vest: Condition 1: No socks, no weight; Condition 2: No socks, with weight; Condition 3: With socks, no weight; Condition 4: With socks, with weight.
Table 2.
Participant Characteristics and Assigned Conditions
| ID | Sex | Age | Height (cm) | Weight (kg) | Added Ingots (#) | Condition Order (1–4) |
|---|---|---|---|---|---|---|
| SC 03 | M | 23 | 172.72 | 82.37 | 41 | 1, 2, 4, 3 |
| SC 01 | M | 23 | 177.8 | 86.18 | 44 | 4, 1, 3, 2 |
| SC 05 | F | 23 | 160.02 | 68.03 | 35 | 3, 2, 1, 4 |
| SC 07 | F | 21 | 165.1 | 52.16 | 25 | 4, 2, 3, 1 |
| SC 08 | M | 23 | 177.8 | 85.91 | 43 | 4, 1, 3, 2 |
| SC 02 | M | 24 | 167.64 | 72.21 | 36 | 4, 3, 2, 1 |
| SC 04 | F | 31 | 167.64 | 75.47 | 38 | 4, 1, 3, 2 |
| SC 06 | F | 22 | 170.18 | 68.03 | 34 | 4, 1, 3, 2 |
| SC 09 | M | 21 | 177.8 | 85.91 | 43 | 1, 4, 2, 3 |
| SC 10 | F | 34 | 167.64 | 58.33 | 28 | 2, 1, 4, 3 |
To ensure participant safety, each participant was securely fitted into a safety harness connected to the Bertec Computerized Dynamic Posturography (CDP) machine. Participants performed motor control tests featuring forward and backward perturbations of varying amplitudes on the CDP machine. These perturbations were categorized as small, medium, and large. Each participant completed three trials for each of the four randomized conditions. During the experiment, the primary data collected included: Latency: Reaction time in response to perturbations. Amplitude: Velocity of participant movement measured on the force plate. This structured and systematic approach ensured the collection of reliable and valid data for assessing motor control responses under varying perturbation conditions.
RESULTS
Effects of Weight and Socks Conditions on Postural Perturbation Latencies:
A two-way analysis of variance (ANOVA) and mixed-effects model were conducted to evaluate the effects of added weight and non-skid socks on postural perturbation latencies. The results indicated that the main effects of the weight condition and the socks condition were not statistically significant (Figure 4). Both conditions produced p-values exceeding the conventional alpha level of 0.05, suggesting no independent effect on latencies. Furthermore, the interaction between the weight condition and the socks condition was also not significant (Table 3), indicating that the combination of these factors did not significantly influence latency outcomes.
Figure 4.
Latency Interactions by Weight and Socks Conditions The linear interaction plot shows impact on latencies based on weight and socks combinations. Here NS stands for No Socks and WS stands for with socks conditions.
Table 3.
Latency Results Between Weight and Socks Conditions
| Weight Condition | Socks Condition | Composite Score (M ± SD) | Medium Right Foot Latency (M ± SD) | Medium Left Foot Latency (M ± SD) | Large Right Foot Latency (M ± SD) | Large Left Foot Latency (M ± SD) |
|---|---|---|---|---|---|---|
| NW | NS | 123 ± 5.8 | 122.9 ± 7.8 | 124.1 ± 7.5 | 122.4 ± 6.5 | 122.8 ± 6.0 |
| NW | WS | 123.9 ± 6.8 | 123.7 ± 8.1 | 124.8 ± 9.3 | 123.5 ± 7.0 | 123.6 ± 7.9 |
| WW | NS | 123.3 ± 7.3 | 123.8 ± 8.7 | 124.1 ± 9.2 | 122.4 ± 9.3 | 122.8 ± 8.8 |
| WW | WS | 123.3 ± 4.9 | 123.1 ± 6.5 | 123.8 ± 5.4 | 122.8 ± 5.9 | 122.8 ± 5.9 |
The mixed-effects model supported these findings, showing no significant main effects for weight condition or socks condition, nor a significant interaction (Figure 4). Random effects highlighted inter-participant variability (Table 3), which was accounted for in the model. The residual error reflected within-participant variability in latency measurements.
Statistical results for weight condition (F(1, 307) = 0.274, p = .601), socks condition (F(1, 307) = 0.409, p = .523), and their interaction (F(1, 307) = 0.887, p = .347) further confirm that neither the addition of weight nor the use of socks significantly alters latency responses during postural perturbations. Latency measurements for different conditions are summarized in Table 3. Mean values and standard deviations (M ± SD) are presented for composite score and latency metrics across conditions.
Effects of Weight and Socks Conditions on Amplitude
Amplitude results demonstrated a significant interaction between the weight condition and socks condition (p < .001). Table 4 summarizes the descriptive statistics, highlighting that the combination of weight and socks conditions influenced amplitude more than either condition alone.
Table 3.
Amplitude Results Between Weight and Socks Conditions
| Weight Condition | Socks Condition | Amplitude (M ± SD) | Range |
|---|---|---|---|
| NW | NS | 6.48 ± 2.65 | 14.00 |
| NW | WS | 5.68 ± 2.40 | 10.00 |
| WW | NS | 6.58 ± 2.25 | 11.00 |
| WW | WS | 6.98 ± 2.69 | 11.00 |
Visual Representation of Amplitude Interactions
Figures 5 and 6 illustrate the interaction between weight and socks conditions on amplitude. The results indicate that the combination of wearing socks and added weight (WS + WW) resulted in a significant increase in amplitude, which implies greater instability and a higher fall risk. Conversely, conditions involving no weight with socks (NW + WS) demonstrated greater stability, as indicated by decreased amplitude.
Figure 1a.
Condition 1: no socks, no weight; 1b. Condition 2: no socks, with weight; 1c. Condition 3: with socks, no weight; 1d. Condition 4: with socks, with weight
Figure 6.
Interaction between Amplitude and each of the Socks Condition
DISCUSSION
The objective of this study was to evaluate the effectiveness of non-skid socks in enhancing balance and stability, particularly during postural perturbations. Since fall prevention is essential in-patient rehabilitation, therapists often incorporate individualized training programs aimed at maximizing strength and minimizing fall risk [4]. If non-skid socks enhance balance, they could be integrated into these programs to improve patient safety.
Our findings demonstrated a significant reduction in amplitude when participants wore non-skid socks compared to being barefoot. This reduction suggests that non-skid socks enhance postural stability, as smaller amplitudes indicate less deviation from the original center of gravity. Our results corroborate previous research by Hubscher and coworkers [6], which concluded that non-skid socks provided stability comparable to being barefoot. Several factors might explain these discrepancies. Unlike Hubscher et al., who tested dynamic balance during gait, our study focused on anterior-posterior perturbations during quiet stance. Furthermore, differences in equipment and testing surfaces could have influenced results. We used a steel surface, whereas Hubscher et al. tested on linoleum tiles. Furthermore, technological improvements in sock design since 2011 may have enhanced grip and stability. Additionally, our COP excursion data indicated comparable performance between non-skid socks and barefoot conditions, aligning with Chari and coworkers[7], who found similar results in specific balance contexts. Further research should explore the comparative effects of modern non-skid socks on both static and dynamic balance tasks.
Contrary to expectations, wearing non-skid socks did not significantly affect latency compared to being barefoot. This challenges the traditional view of proprioceptive feedback, which posits that introducing a barrier between the feet and the ground increase’s reaction time. Our findings align partially with Sun and coworkers[8], who found no significant latency differences among different compression socks during quiet stance but did not test against barefoot conditions. More extensive research on latency with various sock types is warranted to clarify these findings.
Our results showed no significant impact of added anterior weight on either amplitude or latency. This was unexpected, as previous research indicates that carrying external anterior weight increases postural sway and negatively affects balance [9]. Similarly, studies on late-stage pregnancy have reported significant posterior displacement of the center of gravity due to anterior weight[10]. Differences in weight placement, duration of exposure, and load magnitude might explain these contrasting results. We applied a temporary, symmetrical thoracic load, whereas pregnant individuals experience continuous anterior weight shifts over months. Interestingly, the combined effects of added anterior weight and non-skid socks revealed a significant interaction affecting amplitude but not latency. This suggests that the combination of these conditions uniquely influences stability beyond their individual effects. Similar results were reported by Jazayeri and coworkers[2], who examined stability in hospital patients walking with and without non-skid socks. The significant interaction between weight and socks conditions highlights a potential compounded effect on postural stability. While non-skid socks alone reduced amplitude, the addition of anterior weight produced greater instability. This suggests that non-skid socks may be more effective in environments where no additional load is applied.
Several limitations may have influenced our findings. First, our sample size was limited to 10 participants, all of whom were relatively healthy. Larger, more diverse samples could yield results more representative of the general population. Previous research has shown that higher body weight correlates with increased postural instability [11], indicating that participant weight variability might have affected our results. Additionally, our data collection process involved rotating research roles for experimenters, potentially introducing inter-rater variability. Hallgren and coworkers emphasized the importance of consistent data collection procedures to minimize measurement error[12]. Standardized data collection protocols and larger sample sizes should be considered in future studies to strengthen reliability.
Overall, our findings provide novel insights into how non-skid socks and anterior weight affect postural stability. While non-skid socks alone enhance stability, adding anterior weight creates a destabilizing effect, emphasizing the need to consider load conditions when using balance-enhancing equipment. Future studies should explore different load magnitudes, dynamic balance tasks, and long-term interventions to determine optimal rehabilitation strategies.
CONCLUSIONS
Our study investigated the effects of added anterior weight and non-skid socks on postural stability using Simple ANOVA and Mixed-Effects Model analyses. Results indicated that weight and socks conditions had no significant effect on latency, suggesting that neither factor influenced the body’s ability to react to perturbations. However, Simple ANOVA analysis revealed a significant effect of weight conditions on amplitude, indicating that the combination of wearing socks and additional weight increased instability and fall risk. Conversely, participants wearing non-skid socks without added weight experienced a significant reduction in amplitude, suggesting enhanced stability due to reduced deviations from their center of balance. These findings highlight the nuanced role of non-skid socks and anterior weight in postural control. While non-skid socks appear beneficial for enhancing balance when no additional weight is present, combining socks with added anterior weight may increase instability, emphasizing the need for context-specific applications in clinical and rehabilitation settings. Future research will explore a larger, more diverse sample and include populations with varying levels of balance and proprioception, such as older adults or individuals undergoing physical rehabilitation. Investigating different load magnitudes, testing surfaces, and dynamic balance tasks would also provide deeper insights into the clinical effectiveness of non-skid socks. Ultimately, expanding the evidence base on this topic will enable clinicians to make informed decisions regarding the prescription of non-skid socks in healthcare and rehabilitation settings, optimizing patient safety and fall prevention strategies.
Figure 2a.
this is the weighted vest with the metal ingots placed inside each slot; 2b. The non-skid socks that were used in the experiment; 2c. Bertec CDP machine; 2d. the harness that was used when performing the experiment. Harness was used as a safety measure for the participants
Figure 3.
Participant performing the experiment with condition 2: no socks, with weights.
Figure 5.
Interaction between Amplitude and each Weight Condition
ACKNOWLEDGMENTS
This research was fully funded by the “Eunice Kennedy Shriver National Institute of Child Health and Human Development, grant number 1R15HD110941-01”at National institute of Health.
Footnotes
DISCLOSURES
All authors have nothing to declare
Institutional Review Board (IRB):
Chapman University IRB
(714) 628-2833
irb@chapman.edu
Chapman IRB # 22-275
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