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Table 3 Distributions of absolute- and relative strength measures

From: Screen-based sedentary behavior and associations with functional strength in 6–15 year-old children in the United States

  Percentiles Mean ± SE Linear trend for difference across age groups (p-value)a
  10 25 50 75 90  
Absolute Strength
Grip (kg)b
Age Group  
6-9 y 10 12 14 16 19 14.1 (13.7 –14.6) <0.001
10-12 y 16 19 22 26 31 23.1 (22.2 – 23.9)
13-15 y 24 27 31 37 44 32.6 (31.3 – 33.8)
Full sample (6–15 y) 11 14 20 28 36 22.2 (21.5 – 22.9)  
Leg Extensions (kg)c
6-9 y 8 12 17 22 27 17.7 (14.9 – 20.5)  
10-12 y 12 22 30 36 44 29.1 (25.0 – 33.2) <0.001
13-15 y 18 29 41 49 59 40.2 (33.6 – 46.8)  
Full sample
(6–15 y)
11 16 24 37 48 27.7 (23.4 – 32.0)  
Relative Strength
Grip (kg per kg of Body Weight)d
6-9 y 0.37 0.42 0.48 0.55 0.61 0.49 (0.47 – 0.50)  
10-12 y 0.34 0.43 0.50 0.57 0.62 0.50 (0.49 – 0.51) 0.005
13-15 y 0.37 0.45 0.53 0.60 0.69 0.53 (0.51 – 0.55)  
Full sample (6–15 y) 0.37 0.43 0.50 0.57 0.64 0.50 (0.50 – 0.51)  
Leg Extensions (kg per kg of Body Weight)e
6-9 y 0.31 0.46 0.63 0.74 0.87 0.60 (0.51 – 0.70)  
10-12 y 0.31 0.47 0.66 0.77 0.86 0.62 (0.54 – 0.70) 0.020
13-15 y 0.30 0.47 0.65 0.82 0.94 0.65 (0.54 – 0.75)  
Full sample (6–15 y) 0.31 0.46 0.64 0.77 0.89 0.62 (0.53 – 0.71)  
Plank (Seconds)f
6-9 y 15 28 51 72 104 56.9 (52.5 – 61.3)  
10-12 y 19 38 64 92 127 69.7 (64.7 – 74.7) <0.001
13-15 y 29 55 79 121 149 88.6 (80.3 – 96.9)  
Full sample (6–15 y) 18 37 63 91 128 69.9 (66.1 – 73.6)  
Pullups (Repetitions)g       % ≥ 1 (95 % CI)h Mean (95 % CI)h   
6-9 y 0 0.5 2.9 6.5 10.2 81 (77 – 86) 5.7 (5.3 – 6.0) 0.029 <0.001
10-12 y 0 0.6 3.5 7.6 11.9 80 (76 – 85) 6.7 (5.5 – 7.9)
13-15 y 0 0 4.7 10.1 19.5 74 (69 – 80) 9.6 (8.6 – 10.6)
Full sample (6–15 y) 0 0.4 3.4 8.0 13.0 79 (75 – 82) 7.0 (6.5 – 7.6)   
  1. a Linear trends across the three age categories for absolute- and relative strength measures were tested using simple linear regression models accounting for the survey design of the 2012 NNYFS
  2. b Muscle strength was measured through a grip test using a handgrip dynamometer
  3. c A digital hand-held dynamometer was used to measure the knee extension force
  4. d Relative grip strength was estimated as a child’s grip strength divided by their body weight
  5. e Relative leg extension strength was estimated as a child’s leg strength divided by their body weight
  6. f A horizontal body position held with only the hands/forearms and toes touching the floor
  7. g Participants lay on their backs and used their arms to pull themselves up to a strap hanging down 8 inches from the center of the bar
  8. h Due to the large proportion of children that could not complete a modified pull-up, the analysis was conducted using two models: a logistic regression model to test a linear trend in the odds of being able to complete ≥1 modified pull-up with age, and a linear regression model to test a linear trend in the number of pull-ups with age among children that could complete 1 or more modified pull-ups