The Impact of Ski Geometry Data and Standing Height on the Risk of Falling in Recreational Alpine Skiers

Round 1

Reviewer 1 Report

Reviewer Comments

Title: The impact of ski geometry data and standing height on the risk of falling in recreational alpine skiers.

The aim of this study was to evaluate the impact of individual, equipment-related and environmental factors associated with falls among adult recreational skiers. Good introduction where the authors identified a gap regarding the analysis of factors that might prevent the risk of injuries in recreational skiers and not on alpine ski racers as so far. This argument justifies this study. However, as long as I move forward on the paper my concerns were increasing. The materials and methods lacks crucial information especially regarding the multiple regression analysis. Perhaps this lack of information create difficulties for an independent and autonomous analysis of the results. Moreover the discussion section need to be revised since several arguments are difficult to found a clear linkage with the results displayed in table 1 and table 2. Please see y comments bellow.

Introduction section

Line 28. Perhaps could be interesting for the readers less familiarized with ski to define what do you mean as ‘self-inflicted’ falls.

Materials and Methods section

Line 80. A full stop is missing at the end of the sentence.

Lines 112-113. Please clarify for the readers the need of relativize the ski length with body height. What kind of useful information it is possible to capture with this variable.

Line 115. Please explain why it is relevant to calculate a percentage ratio between front and back part of the ski binding.

Lines 117 – 119. Concerning the environmental factors, the authors only described the classification of the snow conditions and weather conditions. However, who assess the snow and weather conditions on each day? Were the skiers based on their individual perception or were the researchers supported for instance on weather forecast specialized websites? We need additional information here.

My other concern was related with the ‘difficulty of the preferred downhill slopes’. I cannot understand how this level of difficulty was assessed. Were based on each skier individual perception or the level of difficulty was measured with any standardized methods (e.g., the ‘colors’ of the ski slopes)? Please clarify this issue.

Lines 134 – 140. Much more information is needed here in order that the readers my fully understand how the multiple regression analysis was performed.

Results section

Table 1

I cannot understand the p-value (.844) on the first line of the table. Could you please clarify which were the variables used for this comparison?

Regarding risk-taking behavior. Could you please discuss why you do not have significant differences? Was not expected that skiers with more risk-taking behaviors will fall more? I would like to read your opinion regarding this result.

Regarding the Relativized Ski Length (RSL) could you please explain what a 95.4 means and why it is different from a 93.1? What sort of information we can extract from the RSL measure? That is why previously on my reviews I asked to explain this measure with more detail.

Table 2

Results from table 2 demands a more detailed explanation. You should not assume that all the readers are familiar with multiple regression analysis. Please provide detailed description regarding the results from table 2. Especially because the discussion is mainly based on the results from this table. Without a detailed description here, readers will experience severe difficulties to understand your discussion.

Discussion section

This section requires considerable work since some arguments displayed here are difficult to make a linkage with the results from table 1 and/or table 2. Perhaps could make sense to start by discussing results from table 1 and then from table 2.

For instance can you explain where in the results we may found evidence for this sentence “A lower age was associated with a decreasing risk of falling in this study” Moreover results from table 1 seems contrary to this. There the mean age of skiers without falls was 38 yrs whereas for skiers with falls the mean was 35 yrs!

Also on Line 192 can you please explain where in the results section is displayed that “A moderate speed decreased risk for falling by about 56%”.

Where in the results section the reader may found evidence regarding this sentence, “A lower relativized ski length was associated with a decreasing risk of falling”.

Between lines 204 and 206 I felt completely confused with your analysis. First, please explain where in the results section we may found evidence for this sentence “An increase in sidecut radius increased the risk of falling by 9% in this study”. Second, in the next sentence you stated that “…the univariate comparison found a significant higher mean sidecut radius in skiers reporting no falls.” Is it my impression or these sentences said the opposite?

Author Response

Dear Editor, dear Reviewers!

Thank you very much for the really helpful comments and all your efforts with improving our manuscript. We did our best and hope to have fulfilled your expectations.

We provide point-to-point answers to the reviewers. All changes made are highlighted in the text.

Best regards

The authors

Reviewer 1:

Introduction section

Line 28. Perhaps could be interesting for the readers less familiarized with ski to define what do you mean as ‘self-inflicted’ falls.

• Thank you. We tried to clarify it in the text as following: “In Austria, self-inflicted falls, i.e. falls without participation of other persons, are the most common accidental causes leading to an injury on ski slopes with 80-90%.”

Materials and Methods section

Line 80. A full stop is missing at the end of the sentence.

• done

Lines 112-113. Please clarify for the readers the need of relativize the ski length with body height. What kind of useful information it is possible to capture with this variable.

• Thank you. We tried to clarify it in the text as following: “Additionally, ski length was relativized by body height as it is well known that a link exists between a greater relativized ski length and a higher risk for falling [7] and/or sustaining an injury [17].”

Line 115. Please explain why it is relevant to calculate a percentage ratio between front and back part of the ski binding.

• Thank you. We tried to clarify it in the text as following: “In addition, a percentage ratio between front and rear component heights of the ski binding was calculated. This standing height ratio relates to the angle of the boot sole when inserted into the ski binding. A previous study has shown that ski boot orientation can influence knee kinematics and would likely alter the loads experienced at the knee [18].”

Lines 117 – 119. Concerning the environmental factors, the authors only described the classification of the snow conditions and weather conditions. However, who assess the snow and weather conditions on each day? Were the skiers based on their individual perception or were the researchers supported for instance on weather forecast specialized websites? We need additional information here.

• Thank you. We tried to clarify it in the text as following: “Participants self-rated perceived environmental factors of the skiing day consisted of snow conditions (fresh snow, grippy, icy, slushy/soft), weather conditions (sunny, overcast, snow fall) and difficulty of the preferred downhill slopes (easy, moderate, hard according to the blue, red and black signs on the ski slopes) [19]”.

My other concern was related with the ‘difficulty of the preferred downhill slopes’. I cannot understand how this level of difficulty was assessed. Were based on each skier individual perception or the level of difficulty was measured with any standardized methods (e.g., the ‘colors’ of the ski slopes)? Please clarify this issue.

• Please see comment above.

Lines 134 – 140. Much more information is needed here in order that the readers my fully understand how the multiple regression analysis was performed.

• We tried to provide more information to clarify hopefully your concerns: “All significant factors (p<0.05) of the univariate comparisons were additionally entered in a logistic regression analysis to estimate adjusted odds ratios (OR) and their 95% confidence intervals (CI) for risk of falls. In addition, significant factors of the simple analysis with more than 2 categories (fitness level, preferred skiing speed, snow condition, weather condition, preferred slope difficulty) were dummy coded (no=1 and yes=2) before entering the multiple logistic regression, e.g. easy ski slope (yes/no) vs. moderate ski slope (yes/no) vs. hard ski slope (yes/no), etc.”

Results section

Table 1

I cannot understand the p-value (.844) on the first line of the table. Could you please clarify which were the variables used for this comparison?

• This p-value showed the non-significant differences between male and female skiers with and without falls according to the Chi-square test. As the overall variable is ‘sex’, the p-value is provided in the same line as the overall variable.

Regarding risk-taking behavior. Could you please discuss why you do not have significant differences? Was not expected that skiers with more risk-taking behaviors will fall more? I would like to read your opinion regarding this result.

• According to our previous studies to this issue, we found that risk taking skiers are mainly skiers with a higher skill level. A higher skill level is associated with a lower fall/injury risk.

Regarding the Relativized Ski Length (RSL) could you please explain what a 95.4 means and why it is different from a 93.1? What sort of information we can extract from the RSL measure? That is why previously on my reviews I asked to explain this measure with more detail.

• Thank you. Additional information to this parameter was already provided in the methods section, see comment above.

Table 2

Results from table 2 demands a more detailed explanation. You should not assume that all the readers are familiar with multiple regression analysis. Please provide detailed description regarding the results from table 2. Especially because the discussion is mainly based on the results from this table. Without a detailed description here, readers will experience severe difficulties to understand your discussion.

• Thank you. We tried to clarify it in the text as following: “Table 2 presents the significant adjusted results of the multiple logistic regression analysis. Age, fitness level, skill level, moderate preferred speed, relativized ski length, sidecut radius, fresh and grippy snow conditions and an easy slope difficulty were found to be factors independently associated with the risk of falling in recreational adult skiers. Risk of falling decreased (OR <1) with a lower age (OR 0.966), a very good/good fitness level (OR 0,251), a moderate preferred skiing speed (OR 0,435), a lower relativized ski length (OR 0.901), and fresh (OR 0,375) and grippy snow conditions (OR 0,451). In contrast, associations with an increase in the risk of falling (OR >1) were found for a lower skill level (OR 2,785), a larger sidecut radius (1,092), and an easy slope difficulty (OR 2,991).”

Discussion section

This section requires considerable work since some arguments displayed here are difficult to make a linkage with the results from table 1 and/or table 2. Perhaps could make sense to start by discussing results from table 1 and then from table 2.

• Thank you for your suggestion, however, main adjusted results were provided via multiple logistic regression analysis. We discussed the results in the order used in the table 2. Where simple and multiple results differ, we tried to clarify this issue in the text. Please see examples below.

For instance can you explain where in the results we may found evidence for this sentence “A lower age was associated with a decreasing risk of falling in this study” Moreover results from table 1 seems contrary to this. There the mean age of skiers without falls was 38 yrs whereas for skiers with falls the mean was 35 yrs!

• Thank you. We tried to clarify it in the text as following: “A lower age was associated with a decreasing risk of falling when adjusted to other factors although the simple analysis found a lower mean age in skiers with falls (table 1). This result of the multiple analysis (table 2) seems to be in contrast to the earlier results by Burtscher et al. [6] and Philippe et al. [7] who, however, also included child and adolescent skiers and snowboarders (Range: 6-80 years) while we only asked adult skiers > 17 years (Range: 18-80 years).”

Also on Line 192 can you please explain where in the results section is displayed that “A moderate speed decreased risk for falling by about 56%”.

• Thank you. Percentage of increasing or decreasing risk is the difference between the result of the odds ratio and 1, e.g. OR = 0,44 (OR < 1 means a decreasing risk): 1 minus 0,44= 0,56 à 56%;
• We tried to clarify it in the text as following in the discussion: “Results of the regression analysis revealed for the factor ‘moderate speed’ an odds ratio of 0,435 which corresponds to a decreased risk for falling by about 56%.”

Where in the results section the reader may found evidence regarding this sentence, “A lower relativized ski length was associated with a decreasing risk of falling”.

• Please see comment above; we tried to clarify it in the text as following in the discussion: “A lower relativized ski length was associated with a decreasing risk of falling (OR 0,901) in the multiple analysis (table 2).”

Between lines 204 and 206 I felt completely confused with your analysis. First, please explain where in the results section we may found evidence for this sentence “An increase in sidecut radius increased the risk of falling by 9% in this study”. Second, in the next sentence you stated that “…the univariate comparison found a significant higher mean sidecut radius in skiers reporting no falls.” Is it my impression or these sentences said the opposite?

• Please see comment above; we tried to clarify it in the text as following in the discussion: “Results of the regression analysis found an odds ratio of 1,092 for the factor ‘sidecut radius’ which corresponds to an increase in the risk of falling by 9%. Mean sidecut radius in this study was 14.5±2.9m (Range: 7.2-27,5m). Interestingly, the univariate comparison found a significant higher mean sidecut radius in skiers reporting no falls, however, when adjusted to other factors, a larger sidecut radius was associated with an increase in the risk of falling.”

Thank you for your effort to improve the paper!

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript is well written and it has a good background with a complete revision of the stet of the art. It has a very large statistical basis (1174 skiers have been interviewed) and data have been correctly analysed. Conclusions are also significant and of interest for the reader and mostly in line with the existing literature.

I would suggest to present some of the data in graphical way (histograms?) instead of having a very long table where too much numbers can create losing of the attention).

Note: there are some typos in the abstract (i.e. environ-mental; individu-al; de-creased), please check the text again and fix them.

Author Response

Dear reviewer 2:

Thank you for your kind revision and suggestions. I am not sure how to use a histogramm for our results of the multiple logistic regression. As reviewer 1 recommended more information regarding results of table 2 in text, we followed his reccomendation. Thus, we abstain from an additional figure.

Round 2

Reviewer 1 Report

Congratulations to the authors. The paper improved. However I felt that in some parts additional information is needed for the reader. Please see my comments bellow.

Line 29

I suggest replace ‘participation’ with ‘influence’.

Line 118

I suggest to replace “…as it is well known that a link exists between a greater relativized ski length and a higher risk for falling…” with ‘…literature display evidence of a positive relation between ski length with risk of falling…’

In the Methods section

This sentence “Percentage of increasing or decreasing risk is the difference between the result of the odds ratio and 1.” that the authors provided in response to one of my comments should be placed somewhere within the methods section. Provide the readers with information regarding how the percentage of increasing or decreasing the risk of falling is crucial for a clear understanding of your results. Additionally these percentages should be added in the paper (please see my comment bellow).

On lines 225-227 for the ‘Individual factors’

The authors present the results this way “Results of the regression analysis revealed for the factor ‘moderate speed’ an odds ratio of 0,435 which corresponds to a decreased risk for falling by about 56%.” I found really interesting the correspondence of the OR value with a percentage (%). Thus, I suggest adding a similar correspondence to all the other factors. For instance, for the ‘Equipment-related factors’ on lines 230-31 the authors wrote “A lower relativized ski length was associated with a decreasing risk of falling (OR 0,901)…” What was the correspondent percentage? For this case, what was the percentage of the decreased risk of falling? Please do a similar analysis for all the factors.

Line 289

The conclusion “…skiing on beginner slopes was associated with an increase in risk of falling.” might lead to erroneous interpretations. This association it was not due to the ‘beginner slopes’ but to the factor that usually in the ‘beginner slopes’ are the lower level skiers which as such fall more. The erroneous interpretation that could be made is that if a high ski level performer goes to a ‘beginner slope’ the risk of falling increases! I suggest to correct this conclusion.   

Author Response

Dear Editor, dear Reviewer!

Thank you very much for the really helpful comments and all your efforts with improving our manuscript. We did our best and hope to have fulfilled your expectations.

We provide point-to-point answers to the reviewers. All changes made are highlighted in the text.

Best regards

The authors

Reviewer 1:

Line 29

I suggest replace ‘participation’ with ‘influence’.

• Thank you, done as suggested.

Line 118

I suggest to replace “…as it is well known that a link exists between a greater relativized ski length and a higher risk for falling…” with ‘…literature display evidence of a positive relation between ski length with risk of falling…’

• done

In the Methods section

This sentence “Percentage of increasing or decreasing risk is the difference between the result of the odds ratio and 1.” that the authors provided in response to one of my comments should be placed somewhere within the methods section. Provide the readers with information regarding how the percentage of increasing or decreasing the risk of falling is crucial for a clear understanding of your results. Additionally these percentages should be added in the paper (please see my comment bellow).

• Thank you! We tried to clarify this in the text: “All significant factors (p<0.05) of the univariate comparisons were additionally entered in a logistic regression analysis to estimate adjusted odds ratios (OR) and their 95% confidence intervals (CI) for risk of falls. We provided for an easier understanding percentage of increasing or decreasing risk of falling which are the respective difference between the result of the OR and 1, e.g. an OR of 0.40 corresponds to a decrease in the risk of falling by 60%.”

On lines 225-227 for the ‘Individual factors’

The authors present the results this way “Results of the regression analysis revealed for the factor ‘moderate speed’ an odds ratio of 0,435 which corresponds to a decreased risk for falling by about 56%.” I found really interesting the correspondence of the OR value with a percentage (%). Thus, I suggest adding a similar correspondence to all the other factors. For instance, for the ‘Equipment-related factors’ on lines 230-31 the authors wrote “A lower relativized ski length was associated with a decreasing risk of falling (OR 0,901)…” What was the correspondent percentage? For this case, what was the percentage of the decreased risk of falling? Please do a similar analysis for all the factors.

• Thank you. We provide percentages and additionally the corresponding OR in brackets for all factors, e.g.: “In this study, fresh snow (OR 0.375) and grippy snow (OR 0.451) are associated with a decreased risk of falling by 62% and 55%, respectively.”

Line 289

The conclusion “…skiing on beginner slopes was associated with an increase in risk of falling.” might lead to erroneous interpretations. This association it was not due to the ‘beginner slopes’ but to the factor that usually in the ‘beginner slopes’ are the lower level skiers which as such fall more. The erroneous interpretation that could be made is that if a high ski level performer goes to a ‘beginner slope’ the risk of falling increases! I suggest to correct this conclusion.   

• Thank you. We tried to correct this as following: “…while skiing as a less skilled skier on beginner slopes was associated with an increase in risk of falling.”

Thank you!

Author Response File: Author Response.docx