Please note that the following activities are dependent on your personal circumstances and whether or not it is safe for you to complete and make sure you maintain social distancing from other people not in your household, as appropriate for your local conditions.
The activities below are based on the principle that:
Speed (meters/second) = distance travelled (meters or m) ÷ time (seconds or s).
If you’re curious, 1 m/s = 2.236 mph.
When we are walking, we can work out distance travelled by measuring our step length and multiplying by our step frequency (number of steps per second). We can use a watch, stop-clock or timer on a mobile phone to record low long it takes.
In the following 3 activities we will explore how we change the timing and length of our steps with altered speed and how other factors like limb posture interact with these.
- Firstly, find a place outdoors with an unobstructed distance of approximately 5 meters or so. The distance doesn’t need to be accurate, a rough estimate is fine, however if you have a tape measure to hand you will get more accurate results. For example, this might be the relative distance between two trees in a park, or between two lamp posts on the street (but not the road safety first!).
- You will also need to have a timer – most mobile phones have a built-in timer
- Have a pen and paper with you too.
- Then walk the 5 meters distance and measure how many seconds this took using your timer. Repeat this process a few times but each time change your walking speed so it is slower or faster. Each time record the time in seconds that it took to walk this distance in the table below. Use the distance and time to measure walking speed (speed = distance/time).
|Speed (m/s)||Distance (m)||Time (s)|
|Walk 1 (normal walk)||5|
|Walk 2 (normal walk)||5|
|Walk 3 (faster walk)||5|
|Walk 4 (faster walk)||5|
|Walk 5 (slower walk)||5|
|Walk 6 (slower walk)||5|
- Now you are now going to change your step length. The objective is to control step length and measure speed and step frequency. The main challenges are to constrain step length without interfering with normal walking style and to make estimated measurements of frequency and calculation of speed.
- For each different trial you will change the step length. For one walk you should be taking longer steps, and for other walks you should be taking shorter steps.
- Measurement of step frequency will be determined using a stopwatch (should be in the same app on your phone as the timer) and recording the time it takes you to take 10 steps. From the estimated step length (Measure this if you can with a tape measure, but if you don’t have one then just estimate) and measured step frequency, average speed can be calculated. Record in the table below.
|Speed (m/s)||Estimated step length (m)||Step Frequency||Distance (m)||Time (s)|
|Walk 1 (normal step length)|
|Walk 2 (normal step length)|
|Walk 3 (longer step length)|
|Walk 4 (longer step length)|
|Walk 5 (shorter step length)|
|Walk 6 (shorter step length)|
- This activity can be completed indoors (you can walk around your home/student halls/bedroom/wherever you feel comfortable) and looks at the ‘economical efficiency’ of human walking. The ability for humans to walk on two legs is a rare locomotory phenomenon, not seen in many other species. When we walk upright, we walk with an extended leg. This means that at some point during our gait cycle, our leg is fully extended (straightened).
- Walk 1. First of all, walk around normally on a flat surface (avoid stairs). Afterwards take some notes about how your legs feel – do they feel tired? Could you continue walking like that for a long time?
- Walk 2. Next, you will need to walk around with a crouched gait. This will involve bending your hips and knees whilst keeping your back as straight as possible (so don’t bend over!) to bring the trunk of your body closer to the ground when you walk. Walk around with a crouched gait.
Afterwards take some notes on how your legs felt when walking like this – was it more tiring than walking with an extended (erect) limb?
- Walk 3. You are going to repeat the crouched walk one more time, but this time bend your knees and hips as much as possible when you walk. Do not extend your legs at any point during walking. Instead try to walk as lowly as possible. Afterwards, write down your experience of walking like this.
- Then compare your notes/thoughts from each of the three walks. Which walk did you find more tiring? Which walk felt like it took more energy to walk that way? Do you think you could walk for a very long distance with a crouched walk? Would your legs feel too tired?
- So, economical efficiency is the ability to walk whilst using the least amount of energy as possible during the movement. When we change our gait from erect to crouched, we are effectively changing the lever mechanics (‘effective mechanical advantage’) of the legs.
What is a lever arm?
A force acting upon a lever arm attached to a fulcrum (pivot) will generate torque, which is quantifiable as a moment (‘rotational force’). The amount of torque generated is proportional to the force applied and to the length of the lever arm. This is expressed by the formula M = F × D, where M is the moment and F the force. D is the distance between the point where the force is applied and the fulcrum, i.e. the length of the lever arm. In the human body, forces are generated by muscles and are applied at the point of muscle attachment on the bone. In a simplified example, the bone will act as a lever arm and the adjacent joint as a fulcrum. Considering the function of the hip abductor muscles (the gluteals, which draw your leg away from your body), the force is applied on their attachment to the greater trochanter of the femur (thigh bone). The lever arm is represented by the distance between the force vector and the fulcrum, i.e. the centre of rotation of the hip joint.
So, what does this mean for a switch from an erect to a crouched gait?
When we crouch our legs, we are limiting the full range of motion of our muscles, and shortening the distance between the fulcrum and applied force which means that many of the leg’s lever arms are generally getting smaller. As a person begins to crouch, the knee flexion lever arm increases whereas the hip lever arm does not change much. The ratio of hip flexion lever to knee flexion lever decreases, making the hamstrings relatively stronger knee flexors. The rectus femoris (shown below) is recruited to help extend (straighten) the knee. Unfortunately, this muscle is also a powerful hip flexor and thus places a higher demand on the hamstrings to extend the hip. This, in turn, produces further flexion at the knee. As higher knee extension forces are required, this will lead to increased energy consumption of the thigh muscle group and will eventually lead to an inability to continue walking in such a manner. This is why your muscles will start to feel fatigued and cramped if you walk with a crouched gait for prolonged bouts of movement.
Similar principles presumably apply to other animals, living and extinct! So dinosaurs, especially larger ones, seem to have moved with straighter, more extended legs whereas smaller ones, including their living descendants birds, moved (or now move) with more crouched legs, because smaller animals can cope with being more crouched and obtain other benefits from crouching such as stability or acceleration.