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NORMAL VALUES
Normal Values
Tongue Elevation Strength Normal Values
Tongue Endurance Normal Values
Lip Strength Normal Values

Qualitative Guidelines for interpreting tongue elevation strength (Pmax)

 
After having carefully studied all of the published studies reporting tongue elevation strength in normal individuals, as determined by the IOPI or IOPI-like methods (see Normal Value References), IOPI Medical offers the following guidelines. See the following section, “Quantitative analysis of tongue and lip strength,” for details.
  • In a normal population, the Pmax falls in about the range of 40-80 kPa, with an average of about 63 kPa. There does not appear to be any consistent gender difference for the elderly and people of middle age. Young males, however, have a Pmax that is 5-10 kPa higher than their female peers. Tongue strength in the elerly is somewhat lower than younger people, having an average that is about 56 kPa.

  • In a normal population, there is considerable variability in tongue strength. The studies show, however, that 95% of normal people, including the elderly, have a Pmax of greater than 34 kPa.

  • Tongue exercise can increase Pmax, but the increase will probably be small unless the patient’s tongue is relatively weak to start with.

  • Some evidence shows that increases in Pmax resulting from tongue exercise are associated with improved swallowing (see Robbins et al., 2007, Reference #22). More research to document the efficacy of tongue exercise is needed, however.

Quantitative analysis of tongue and lip strength

Tongue Elevation Strength Normal Values:

There are currently 10 published studies that have reported means and standard deviations of tongue elevation strength in normal populations of men and women (see Normal Values References below). Some studies were entirely dedicated to establishing normal values while others were primarily focused on disease states, but the latter all had normal control groups that provided data on normal values. Altogether, 768 subjects were studied.

The subject pool can be separated into three age groups:
  • Young subjects between 20 and 39 years of age,
  • Middle-aged subjects between 40 and 60 years of age, and
  • Old subjects greater than 60 years of age.

There was no consistent gender difference for middle aged and old subjects. Because the gender difference was either inconsistent or absent, male and female results have been combined for the following table:

Study Young (20-39 yr) Middle Ages (40-60 yr) Old (>60 yr)
Mean SD Num Mean SD Num Mean SD Num
Stierwalt, 2007 62.02 13.9 95 60.42 12.25 45 55.01 14.32 60
Lazarus, 2000       60.5 12.75 13      
Youmans, 2006 63.9 15.2 30 61.5 13 30 54.5 11.3 30
Lazarus, 2003 66.17 11.18 31            
Youman, 2009 75.42 15.56 32 70 14.14 32 60.12 14.14 32
Clark, 2009*       60 10 39      
Solomon, 1995             69 10.6 19
Robbins, 1995 64.5 8.54 10       49.5 11.22 14
Solomon, 2004 61.6 8.37 10            
Clark, 2012 55.8 13.5 68 62.8 13 60 51 15 43
Weighted value 65.73 12.95 226 62.44 12.21 159 57.42 12.97 155
*baseline tongue

When calculating the Mean and SD across all of the studies, the values from individual studies were “weighted” by a factor that was directly proportional to the number of subjects in that study. This was done on the assumption that a study having a large number of subjects was more “powerful” than a study having a much smaller number of subjects in estimating the actual mean of the entire “Normal Population.”

The weighted Mean and SD of each age group, looked at across all the studies, was used to create a Normal Distribution curve. The three curves from the different age groups are shown below.

Tongue Normal Value Graph
Tongue strength values corresponding to various percentiles from the estimated normal distributions are shown below. It is common to consider values below the 5th percentile to be “abnormal.”

Group Tongue Strength (kPa)
1% 5% 10% 20% 25% 50%
Young 31 41 46 52 54 63
Middle 34 43 47 53 55 63
Old 25 34 39 44 48 56

Tongue Endurance Normal Values

The data are as yet insufficient to assume the statistical normality of the endurance distributions in the normal population, so an estimate of a normal probability function is not yet warranted. However, the studies published so far suggest an average endurance of about 30–35 seconds for the tongue. Endurance times of 10 seconds or less would be an indication that a patient probably has low endurance. In such a case, it may be useful to consider that fatigability is a contributing factor to this patient’s oral motor problems.

Lip Strength Normal Values

An estimated normal probability distribution of lip strength of a group of 171 normal persons, aged 18-89, is shown below. Although there were no consistent age differences, there was a pronounced gender difference.

Lip Normal Value Graph
Data are taken from Clark et al., 2012, the only current study reporting pressure measurements of lip strength that has reported on gender effects. The “cheek method” (see Lip Strength) was used in this grpah of lip strength.

For Normal Value References click here.