Pretty cool info about calculating resistance when doing body weight movements. Particularly useful if you track by volume (number of total reps x weight lifted) like I do
Calculating Actual Resistance: Incorporating Percentage Bodyweight into Weight Training Workloads
Many exercises utilize a portion of the bodyweight along with the added weight. For example, during Barbell Squats, the weight of the upper body and a portion of the upper thigh are lifted in addition to the added weight. This is very similar to what occurs in the Deadlift. Although the upper body is angled forward at the bottom of the lift, it is lifted upward more directly against gravity along a very similar path as the added weight. In contrast, the thigh rotates from a more horizontal position at the bottom of the lift to a vertical position at top, moving less directly upward against gravity.
So, how can we accurately calculate the bodyweight used as a load for these exercises?
de Leva's Segment Weight data
Segment Quantity Percent Extension
Head 1 6.810 6.81
Whole Trunk 1 43.020 43.02
Total Arm 2 4.715 9.43
Total Leg 2 20.370 40.74
Total Percent: 100
Using normative data for the
percentage weight of body segments, we can calculate the weight of the move more directly upward with the weight (upper body). Using
center of gravity of body segments, we can calculate torque required to turn body segments from near horizontal to near vertical.
Squatsor
Deadlifts
Step 1
Calculate weight of body segments that share similar center of gravity and move mostly upward with added weight, in this case upper body
Method A: Head + Trunk + 2 Arms = ~59.26% of total bodyweight
Method B: Total Body (100%) - 2 Legs (40.74%) = ~59.26% of total body weight
Step 2
Calculate torque from heavy body segments that rotate significantly against gravity, in this case, torque from both thighs.
Weight of 2 Thighs * Thigh's Center of Gravity from Knee
From
body segment data we know:
Weight of Thigh = ~11% of body weight
COG of Thigh = 0.43of segmental length measured from proximal end (from hip)
So we need to sum the weight of both legs and determine the COG from the opposite end
= 11% (2 Legs) * (1-0.43)
= 22% * 0.57
= 12.54 % of total body weight
Note: We would end up with 17.79% if we had used de Leva's data.
% Body weight used = % weight of 2 thighs * COG from knee = [(2*14.47%) * (1-0.3854) COG] = 17.79%
Step 3
Add resistive forces of upward moving body segments (steps 1) to torque forces of upwardly rotating body segments (step 2). In this case, we add the weight of the upper body with the torque from the thighs.
Percentage of body weight used as a load during Squats or Deadlifts = ~72%
Note: Using de Leva's data in step 2, total percent bodyweight would be approximately 77%
59.26% + 17.79%
Here are other examples of exercises using only one leg:
Step Ups or
Single Leg Squats
Upward Moving = Total Body (100%) - 1 Leg (20.37%) = 79.63% of total body weight
Upward Rotating = Thigh Weight (11%) * Thigh COG (0.57) = 6.27%
% Body Weight used = Upward Moving (79.63%) + Upward Rotating (6.27%) = ~86%
Notice when Step-ups are performed with heavy weights, the lower leg assists in the initial push off, the hardest part of the movement. Never-the-less, the lower leg rises more directly against gravity with the body and added weight, whereas, the upper thigh rotates against gravity.
Notice other exercises like the Split Squat and Single Leg Split Squat appear to only use a single-leg exercise, but actually use both legs to lift the weight or at least the weight of the rear leg rests on a surface. On these particular exercises, the upper body and thigh of rear leg travel upward, whereas, the leg of the exercising thigh and the shank of the rear leg both rotate upward.
Split Squat or
Single Leg Split Squat
Upward Moving = Total Body (100%) - 1 Leg (20.37%) - 1 Shank (4.57%) = ~75% of total body Weight
Thigh Rotation = Thigh Weight (11%) * Thigh COG (0.57) = 6.27%
Shank Rotation = Shank Weight (4.57%) * Shank COG (0.57) = 2.6%
% Body Weight used = Upward Moving (75%) + Upward Rotating (8.87%) = ~84%
Generally speaking, to calculate the percentage of bodyweight lifted upward, simply add up the percentages of all the body parts that are moving (or not moving) directly against gravity. If all but a few segments move, simply subtract the percentages of the segments that are NOT utilized from 100% (total body) to arrive at the percentage. Notice the percentages for the arms and legs are only for one each, so if both limbs are utilized, you will need to multiply by two.
Next, identify body parts that rotate upward significantly against gravity. Calculate the torque by multiplying the center of gravity of the body segments (from the fulcrum) by their respective segment weights.
And finally, add the resultants to determine the percent body weight contributing to the exercise's resistance.