Near-Infrared Spectroscopy- How It Works




Engineer Your Way to 10,000 Steps a Day

Many people are trying to get 10,000 steps or more in each day to become somewhat active. Whether getting in those steps will help to be healthy or active, the use of a pedometer will help to count those daily steps. Today it is hard for me to find a person who doesn’t have a Fitbit or other step counter on their wrist. So, what is their device really doing?

Fitbit Alta, a pedometer used to count steps, calories burned, and miles walked daily.

Pedometers use accelerometers to measure changes in velocity of the forces your body produces. The use of accelerometers is becoming increasingly popular in technologies for more than just pedometers. For instance, detecting car crashes to release the airbag, or turning off the hard drive when your laptop falls to prevent damage. There are many different features to consider when choosing the correct accelerometer for your specific application.

Accelerometer board designed to measure movement in the x, y, and z axis, another factor to consider when designing a pedometer. 

In the case of a pedometer, we want to know: how do we design an accelerometer to accurately count the movement of someone taking a step? We want the pedometer we use not to over count or undercount our steps. It needs to be sensitive enough to detect when we move enough, but not overly sensitive to count a sneeze as a step. There are many variables in an accelerometer to design it to your needs. In this case, adding a low pass band filter will help us to accurately count the steps we want.

In designing our accelerometer, we want to choose our maximum swing. This will be in the form of g, or acceleration due to gravity, 9.81m/s2. When measuring sudden stops and starts, you want a higher g, such as 5g. When measuring the earth’s tilt, only  1 is needed. Since we want to measure the movement of somebody walking, typically 2g is used.

The resolution of the accelerometer will determine how it will detect the smallest increment in acceleration. If you would like to improve the resolution, then you can do this by using a filter to lower the noise and bandwidth. The resolution can be given by the equation:

R=N x √(BWlpf x1.6)

Where R is the resolution, N is the noise density and BWlpf is the bandwidth of the output low-pass filter.

A few things to note: N is in the units µg/√Hz and the bandwidth is what we want to solve for to improve the resolution of the device. If I want to design an accelerometer with a 13-bit resolution, so that even low walking speeds are accurately measured, that would be the equivalent of an R value of 4mg. Based on high performance of pedometers with maximum swing of 2g, we will choose N to be approximately 120µg/√Hz.

Solving for BWlpf using basic algebra, we find that BWlpf=(R/N)2/1.6

Plugging in the values of R and N, we find that we want a bandwidth to allow for the frequency of about 695Hz.

Depending on the design of the accelerometer, there would be different values of N and R. For instance, certain companies may want higher resolution and may be able to get a different noise density based on their maximum swing and other factors. They would be able to choose the type of bandwidth filter based on their needs and adjusting the equation accordingly. The bandwidth of the filter used in designing the resolution of the accelerometer for a pedometer is just one of the many variables and problems an engineer would consider when designing a device to track steps.


Further Reading:

Photo Sources:

Skiing Imitating Apparatus

Spring Biased Ski Exercise Mounted On Adjustable Inclined Slope

Patent US3591172A filed on October 3, 1968
Issued: July 6, 1971
2.5 years to issue
Inventor: Franz Hude
US Classification: A63B69/18
10 Claims

This patent is a device used to imitate the movement performed when skiing. It consists of ski replicating members attached to a base that remains stationary. The rear ends of the skis pivot side to side to mimic the motions done while skiing. There are springs that attach the front of the skis to each other to provide resistance. There are also springs that connect the rear of the skis members to the rear of the base. A waistband is included in the device to give the user security and balance. The user can adjust the angles of the skis as well as the resistance applied. The device is meant to replicate the forces applied to a skier when executing different skiing drills. The user is required to adopt proper skiing positions and therefore the appropriate muscles, including the legs, hips, and ankles, are trained correctly when they use this device.

Figure 1: The user stands on the skis facing the narrow end of the base.

Someone who is interested in skiing both competitively and recreationally may be interested in using this technology. I think that if someone has never skied before and is nervous to get on a slope, this device might give them the confidence they need to get started. Older people who have never skied before and are self-conscious because they would be surrounded by other skiers who maybe started at a younger age may find this device helpful. It would also benefit professional skiers in the off season to prepare themselves and their muscles. Considering the device can be used anywhere on a flat surface, snow is not needed for someone to train in skiing. It may even be beneficial for coaches to be able to critique and give pointers to skiers while they are on the device after watching them practice.

The technology of this device includes springs, slider bars, and low friction material. The base also consists of several support pins and sockets to ensure the proper support of the apparatus, the correct amount of pivoting, and rotation. The springs that attach the front ends of the skis together provide the resistance necessary to allow the skis to rotate away from one another. The springs that connect the rear end of the skis to the back of the base provide the resistance a skier experiences when rotating about its longitudinal axis. The user can add more springs or remove them to change the resistance. The backs of the skis are attached to a bar that is elevated so the user is at a vertical angle. This incline can be adjusted by the user by sliding the slider bars forward or backwards, raising the back of the skis or lowering them. The underside of the ski members have a convex shape and are made of low friction material to easily pivot.

This device is novel in how is activates the same muscles involved in skiing as well as the movements involved. Previous devices have been designed to mimic the movement and perhaps give the user practice on balance, but they do not give the resistance that a skier would experience on the slopes. For example, Raymond E Armstrong designed a skiing simulator device that had skis on two treadmills which gave the user a chance to get a feel for the movements without fear of falling, but did not provide the challenge to the muscles that would be used.

I chose this patent because it wasn’t something I had seen before and thought it was a good idea. I personally have always wanted to ski or snowboard as it seems like a fun activity. However, I have also always been scared to fall or just be plain bad at it. I think that if I had access to this device I might feel more confident if I know the proper form I should have and my muscles were prepared for what they would feel in the actual snow. I also think that it would be a fun and different form of exercise as opposed to the boring elliptical or rowing machine.

Free Weight vs Machines: Is One Better Than the Other?

Searching for the best possible way to make gains in the gym can often be tricky or overwhelming. When you walk into the gym you can probably find a wide range of weight machines along with rows of dumbbells and squat racks. Many lifters incorporate a mix of free weights and machines when they are training. Free weight exercises require balance and they allow for movement in multiple planes while weight machines provide movement over a fixed range of motion. Some people swear by free weights alone and wouldn’t dare touch an exercise machine at the gym. Others solely use weight machines in their workouts. Which method of lifting is the best way to get in shape?

The benefits of using weight machines are that they are easy to use and figure out which is especially helpful for beginners. They are considered “safe” in the sense that you will not drop a heavy weight on yourself or someone. It is also easier to change resistance and loads on a machine. However, the movements one makes on a weight machine do not imitate natural movements we make every day. The exercises done on a weight machine usually do not target large muscle groups so isolated training is required.

The advantages of free weights are that they mimic real world movements and they target larger muscle groups, working more muscles in one exercise at a time. They require the use of stabilizing muscles so one must balance to perform the exercises. This coordination is part of the reason they are more natural movements that can help in day to day activities. Common disadvantages are that they are intimidating to beginners and some exercises require a spotter.

Lifters often quantify their strength by their one repetition maximum (1RM) or the heaviest weight a muscle/muscle group can successfully lift just one time with correct form. A study published in the Journal of Strength and Conditioning compared the force produced by muscles when squatting and bench pressing free weights or in a Smith machine. The results showed that participants had a greater 1RM in squatting with a Smith machine. Alternatively, participants had a greater 1RM when bench pressing using free weights. A previous study comparing free weight squats and bench press to machines showed greater 1RM in machines than in free weights, however the differences were not significant.

Example of a man squatting under a smith machine.

Another study done by Schick et. al. (2010) was conducted to compare the activation of muscles when bench pressing on Smith machine or a free weight bench press. The results found that there was significantly greater activation of the medial deltoid in the free weight bench press than in the Smith machine bench press. The instability caused by the free weight bench press requires more use of medial deltoid to both stabilize the body and produce the force necessary to lift the weight. The results did not show differences of activation in the larger chest muscles. The study used experienced and inexperienced lifters to determine whether one exercise was better beginners or not, but they did not find any significant differences between groups. It should be noted, however, that the study defined experienced as someone who consistently benched twice a week for 6 months. It may have been more helpful to use subjects with some more time and experience lifting.

The studies conducted do not necessarily favor any mode of exercise over another. I believe that more experiments should be performed to study the long-term effects of using free weights vs machines and whether one method may lead to faster results.

When deciding on whether to choose to lift using free weights or machines, it is best to determine what your goals are. If you want to be more efficient in the gym and use the most muscles in less exercises, free weights are your best bet. If you do want to isolate certain muscles and have more time to spare weight machines will work well. Many people incorporate both free weights and machines in their workout regime. I think it is most important to keep in mind that free weights are safe and activate more muscles when performed correctly. While weight machines may help in making you stronger, they avoid working those stabilizing muscles to help with balance. So, when your buddy needs help moving his couch up 3 floors to his apartment, you might wish you trained with free weights instead.


Recommended Further Reading:

A Comparison of Muscle Activation Between a Smith Machine and Free Weight Bench Press

Comparison of muscle force production using the Smith machine and free weights for bench press and squat exercises.

Training Principles: Evaluation of Modes and Methods of Resistance Training

Comparison of One Repetition Maximums Between Free Weight and Universal Machine Exercises

Strength Training: Free Weights or Machines?

Roundtable Discussion: Machines Versus Free Weights